Why do stores keep Betta fish in small containers?

No fish can be alive for long in a container with no filter system. Everyone who knows about aquarium nitrogen cycle should know this.

Betta or Siamese fighter fish is a tropical fish species. They need water temperature of 78F+. Any lower temperature might result in weakened immune system. They can't live for long without a filter either.

Small betta cups at pet shops are no place for any fish. The pet stores do not care because they hope to sell the betta before it die. The cheap wholesale price makes it still profitable for them even some betta are dead on the shelf which is often the case.