Why are bettas typically kept in room-tempature water?

Hello everyone,

There's something that has always puzzled me about bettas. From what I've
read, not only are they tropical fish, but they actually prefer higher water
temperatures than most tropical fish. So why are they typically kept in
room-temperature water? Is it because they're more adaptable than most
tropical fish? Or did someone at one point say "Well, they're very elegant,
colorful, attractive, they tolerate low levels of oxygen fairly well,
they're not very active and don't produce much waste. They'd be perfect for
selling to people, who could keep them in small, unfiltered, stagnant bowls.
A cheap, convenient pet for customers, and very lucrative for us. So what if
they live in warm water? Adding a heater to a small container costs more and
isn't as convient. Not as many people would buy them if we told them they
need the heat. So let's pretend bettas can tolerate them and let people
treat them the same  nasty way they treat goldfish"?

Now, if people are under the delusion that just because bettas tolerate
smaller spaces better than most they do just fine is small jars, is it the
same thing for temperature? I mean, is keeping them at room temperature also
a form of abuse? It is just a commercial thing that disregards the comfort
of the fish, or are bettas really more tolerant of colder water than most
tropical fish, despite their natural preference for warmer water?

Also, assuming a betta is relatively tolerant of room-temperature water
(after all, some do manage to live a few years in there, though whether
they're happy is another matter), how well would it take a transfer from a
heated tank to colder water? For instance, if a pet store keeps some bettas
in heated tanks (where they really should be kept), as some do, and then a
customer buys one to keep in a unheated bowl, does the betta have a good
chance of adapting reasonably well, or will it be a nasty shock for it? It
seems to me that any radical change in temperature isn't good news for any
fish.

What about a betta that's used to colder water who gets transferred to a
warmer tank? The warmer water is closer to the betta's natural habitat, but
what about the temperature shock? If it lives it may get used to it and
actually be happier than in his old container, but isn't the transition
traumatizing for the fish?

Anyway, maybe I'm wrong and bettas actually don't mind typical goldfish-like
conditions. But I'd be very interested to know what people think about this.