Why do people end up collecting/buying so many lenses?

Different reasons. Some people do it because they are gearheads and/or its fun. Others do it because they need to.

As far as your comment about only needing 2 lenses, that's not correct. You really only "need" one lens. Some people need a lot more (pros in particular). Some people hate zoom lenses (I prefer prime lenses, as annoying as it can be to change them while shooting). I do have a couple of zooms for those times when I need the convenience.

Some people may have a favorite lens that isn't fully functional on their new camera, so they need to get one that is (and simply use their old lens for certain situations).

Also some people like to have back-up lenses (I almost learned the hard way when one of my lenses failed on a trip overseas. The next day was a sunday so everything was closed. the following day I was in a small city/large town - I was fortunate enough to find the only camera store in town, which had what I needed)

Your asking a good auto, motorcycle or airplane mechanic to have 2 tools. A adjustable wrench, and a hammer.......

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To a seasoned photographer, our lenses are like tools are to a master mechanic. We, like them, have specialized tools to do a specific job, and do it - right.

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Lenses are almost more important than the camera body... In fact, they are..!

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Many lenses today have "close focus". But "close" won't cut it when you need to really show off the diamond on her finger in the wedding album. Screw on glass magnifying lenses, while they will get you much closer, don't hold a candle to a actual macro lens. Need REAL close, get a macro lens with a built in ring light or add the ring light when needed.

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Telephoto..? Same here. Your zoom lens may go to 200 or 300mm but compare it to a prime 200 or 300 and there is no contest. Same with the wide part. Your lens drops down to 18mm (but is part of a zoom) but the image wont look the same with a 18mm prime.

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Oh, we have zoom lenses. But, we know the IQ - Image Quality - of "other lenses" is over and above the zoom, so we have and use them more when needed .. A zoom is a adjustable wrench or a 3 pound ball peen hammer. It will get the job done but at what cost to the image..? A prime lens has contrast and crispness many or most zooms don't. A zoom has many internal lens elements. Each adding it's own flaw to the image. AND, many are moving... No, lenses are NOT made equal. Manufactures know this and know most people don't or won't care, or know the difference. However, even the worst zoom or cheap lens gives you a image and many - take it.

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A set 500mm will be a lot sharper than a 50~500 @500. A lot..! My 85mm f/1.8 delivers way better images than my 18~200 set at 85. My set 200 is much sharper too.. Then there is the f - stop factor. Many primes can be had in large f/stops zooms will never have and if they did, would be soooo expensive as to be un-real. Not to mention how good the IQ is.

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Low light, fast action..? Zooms, normally are 3.5 and up.. A 300 f/2.8 is awesome beyond words. A 55mm f/1.2 can see in the dark..! A 85 f/1.8, well.. again, There aren't too many words here that can explain.

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We collect lenses to do a special job, like a mechanic has special tools for his jobs. Often these tools can cross pollinate, some not. However, if the demand or desire is there, we would rather add another quality piece of glass to our stable of lenses than give our clients a half good job.

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For your kind of photography and most other people, sure, "you may only need 2 lenses a decent zoom (50-200mm) and a wider angle lens" .. but for the rest of us, that ain't gonna cut it one bit.

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There IS a difference between just wanting to take pictures and make money. Thats why some of us are on one side of the fence and others are out in the pasture, looking....

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Don't be afraid to buy good glass.

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It all depends on what you are shooting. In reality, many people can get by just fine with one or two good quality zooms, covering the range of somewhere in the 20-30 through a 200-300 range.

However, the longer someone is involved in photography, the more likely they will want to expand into other areas.

I currently own 4 lenses, but use two of them for 95% of my work. One is a 24 - 70, 2.8. The other is a 70 - 200, 2.8. I also have an 85, 1.8 and a 100 macro . . . I use them, wouldn't be without them, but don't use them often.

And then there is the "wish list" for a true wide angle, a fish eye and something in the 300-400 range.

You can do much with a hammer, screwdriver and a pair of pliers. But a true mechanic will have a toolbox (or toolboxes) full of wrenches, sockets, as well as an assortment of tools to match his or her needs.

I have an 18-200mm zoom and use if for a walkaround lens. BUT, as a sportsphotographer, I need the longer reach of my 135-400mm as well as the speed of my 70-200mm f/2.8. For low-light situations, I'm looking at a 17-55mm f/2.8, an use my 35mm f/1.8 and 50mm f/1.8 for the best brokah.

My brother does wildlife photography and pulls out his 500mm at times, while his macro lenses give him amazing views that my lens collection can't provide.

I just shot a party and was limited by my 18mm wide and am now looking for a 10 or 12 mm to compliment my lenses.

How many different lures does a professional fishman use? How many spices for a great chef? You can do well with limited resources, but there are worlds you haven't discovered - - - yet.

By the way, most of us don't buy and sell lenses. We build our "toolbox", one lens at a time.

There are times some lenses are used. And if a person can afford it, he can buy one. Otherwise I would rent one.