Why aren't Sony cameras as popular as Nikon and canon cameras?

Sony just started in the dSLR market in 2006. Considering that they are new, they are doing just fine.

And, they are the most popular camera in the world, but not all people know it. They are now the number one maker of image sensors. Sony image sensor are found in cinema cameras, TV/broadcast, dSLRs, not just Sony, but all Nikon dSLRs, now all Pentax, just started with Olympus, Leica X2, and every image sensor in the iPhone 4, 4s and 5 are all Sony.

Sony owns the mirrorless market, nobody has a better image sensor. So now things are changing. It will be a few more years before people are totally broken out of their Nikon, Canon, Coke/Pepsi thinking. and it's already happening.

4 years ago when I started answering questions, people never asked about Sony, it was always CaNikon, but now not only do people ask about Sony, they know the model numbers of the various mirrorless or new dSLTs, so that's a huge difference, even Pentax is getting a little more love now that they are using better image sensors.

Sony is not as well established as Nikon or Canon. And although many cameras use Sony sensors, that is just a single electronic part, and actually produced by a different division in the Sony conglomerate.

Also, a sensor in itself does little. The "magic" in the camera is the processor that converts the signal from the sensor into a photo. That is where Sony is lacking behind Nikon and Canon; they just don't have the experience as the others to make high performance processors.

And as you indicated, the lens selection is lacking with Sony. Their lenses are more or less consumer-grade, and they lack the high-performance professional lenses that Canon and Nikon have.

Finally, Sony is putting their future into the NEX/Mirrorless cameras, so their DSLRs are not their future focus.

Having done a career in television news / sports photography - nearly 30-years worth, I can tell you that Sony is, and has been, the brand of choice for television stations and networks around the country.

Sony is not well known for consumer level still / video cameras but Canon and Nikon are and have been chosen by professionals around the world for many years.

Today you'd be hard pressed to find a professional using Sony still camera gear, they're just not the brand of choice.

In the 60's Nikon came up with a promotional plan. They offered the free use of camera lenses to any professional that used their camera bodies. In exchange they could say that Nikon was the camera of choice for the professional. After that they became the camera of choice. It's name brand recognition more than anything else.

Sony is relatively new to the dSLR market. They had to acquire Minolta just to jumpstart their technology. Sony however is not new to making digital cameras. Their Mavica is considered to be one of the pioneer digital cameras. For a time even, Sony has been contented producing and supplying digital sensors to other companies.