We keep many fish that are terribly unsuitable for aquariums... Pacu, RTCs, etc. Not all sturgeon get gigantic, many of the ones you see for sale are hybrids, often with the smaller Sterlet to increae the temp. tolernace and limit adult size.
Wait a minute. No to long ago a LFS had small sturgeon for sale. They where about 6"long and like 16.99. But why would anyone want a fish that get large like that and lives a 100 years?