Why are drinks made when you order them?

Anything fizzy will go flat. Alcohol evaporates over time. People order drinks different ways. Making them to order really doesn't take that much time

They go flat and won’t be fresh

Depends on the drink.

to make sure the alcohol doesn't sink to the bottom and you're getting the right portions of each ingredient

They are better very fresh.

for several reasons.

Where to store all those pitchers of various drinks?

the soda would go flat.

I live in Las Vegas, known for its bars and liquor service and souvenir container drinks up to a yard long. There are machines serving frozen drinks with the alcohol already in them, and an extra shot can be added for a dollar usually. You can go to a supermarket or others selling alcohol packaged with pre-mixed alcohol containing drinks in sealed containers, ready to pour over ice or put in your freezer. You can make a party with a bunch of these. And, a bartender may mix a few of the same drinks in a large shaker and pour two out of one container.

But, if a drink is with ice, the ice melts. Sodas lose carbonation. There are thousands of possible drinks that a bartender can prepare. Open containers and pitchers can get contamination sitting out. There are layered drinks and some ingredients may separate while sitting after mixing. Bartenders here make most of their money on tips, custom-making each, sometimes with "flair".

https://www.youtube.com/watch?v=AWSzsjUh5o8

I was in Mainland China, and bartending was a very mechanical job that they didn't like, at least a long time ago.

A bartender in most places is a service job, appreciated and some have discretion of how much liquor to put in drinks, with minimum as a standard shot. Others are pre-measured or require measures.

I gamble at bar slot machines and am given special treatment with my simple Skyy Vodka and orange juice.

When I walk in, they will clear non-gamblers from any machine I want. They pour my drink before I sit down as soon as they see me. They make it extra strong, the way I like it. A couple of places with large and small glasses know I think the small is too small and large too large, so pour mine in a large glass leaving an inch unfilled. They pour me a new one whenever the glass is almost empty. The drinks are on-the-house for me covered by gaming and I tip $2 a drink and more if I win. Naturally, I lose more than I win over time, and it's cheaper to buy them without gaming, but I'll walk away sometimes with a couple of hundred dollars more than I arrived with.

I'm not even a big gambler, but I'm consistent to gamble. I'm not the only one and I don't gamble what I can't afford to spend. It would not be the same with pre-poured pitchers.

Because the liquor in what you've premixed can be used to make something different, and if you've used it all up, you can't sell any of those other drinks.

For instance, let's say you want to pre-mix gallons of Bloody Mary, ready to serve. And you use up all the ingredients to do so. But then someone wants a Vodka Martini. You can't sell them one, because all your vodka has been tied up in your pre-mix.

Mixing up enough pre-made drinks to cover everything your customers might order would actually take quite a bit MORE liquor than just leaving it in the bottles and mixing them to order.

Some drinks aren't goo after a while; also, if nobody orders drinks that have been made, they may need to be thrown out: a waste.