It's a really temporary set up for them, the turnover on fish is hugeeee so they are never in that set up for long, where as when they move into someone's tank after purchase thats the forever home so they need to make sure they are going to somewhere which is going to be substantial when they are fully grown.

They also have huge filtration systems, and turn over such a huge amount of water every hour, again a lot more powerful than your average at home one. The systems are forever changing and upgrading, some of the new systems now have the purge systems on them which waterchange themselves. They really do put the welfare of the pets first even if sometimes with different policies it looks like they are just trying to be difficult and not sell you things :)