Actually Nurse Sharks do very well in captivity - provided that they are given enough room. They have even been known to breed in captivity on many occasions.
But it's true that they aren't generally suited for the vast majority of private aquarists. Unless you have enough space for a good size swimming pool indoors - a private aquarist should never consider keeping a nurse shark.
And the biggest problem - is LFS often have Nurse Sharks, either for sell on on display - which can make aquarists that aren't very knowledgeable think that it's an ok species of shark to keep - when in fact it isn't.
IMPO - the following sharks shouldn't be available for sell thru LFS - Nurse sharks as well as any requiem shark - including Blacktip & whitetip Reefs, Lemons, and Bonnetheads.