I've been dip netting and keeping minnows, darters, shiners and other fish I've caught since I was a kid. It's something that my kids and I do as well. Most states you just need a fishing license.
I know I'm super late to the thread, but I think a big reason is legality. In a lot of places it is illegal to keep native fish. I think another big reason is that these fish can get very big and produce a lot of waste and not many people can afford to have a couple hundred gallon tank to keep a school of sunfish, a LMB, bullhead catfish, etc.