Artists rarely ever did - it was even rare back when Tupac did it. One day while Tupac was filming (either Gridlock'd or Gang Related) he caught a kid listening to the explicit version of his album and Tupac went over to him and said something to to the tune of "man, you're too young for that. I put a lot of effort into making the clean versions they're entirely different takes, you should be listening to those" - not the exact phrase, but something to that tune (You'll have to read over 10 books on Tupac to amass the wealth of knowledge I hold on his life)
Anyway, the reason it doesn't happen anymore is because studio expenses make up too large a portion of the expenses for them to justify having dude going in their to re-do all of his takes