Why do stores keep Betta fish in small containers?

I have kept 100s of Betas in glass decorative containers for years, they lived for years. I had one live for about 5 1/2 years in one. If your house is warm enough, the Betas will live just fine, mine sure did. The only problem I have ever had with Betas dying, is my Autistic son eating them straight from the bowls. I fixed that real quick, though, only lossed 5 out of 30 that way, until I explained in a way how nasty that is, and working God and Christ into it because he loves religion and God and Christ.
So someone who has kept 100s of Betas this way since I was 10 and will be 28 next week, I think my Mother, Evelyn, and I know what we are doing.