Because he is a great and beloved President.Shouldn't be that hard to figure out.He balanced the budget ,kept us out of wars and left Bush a budget surplus(which he turned into a 1.2 trillion dollar deficit)
Even members of the GOP ( the sane GOP, not this current bunch) like Clinton. He is going to live to see himself ranked as one of the top ten Presidents of all time.
Everybody is nostalgic for the 90's. Well, except for the repubs. They're nostalgic for the 50's and that's their problem. People want to take a ride in the Way Back Machine to forget their current trials and tribulations, just not that far back.
The Tea Party GOP wants to go back to the 50's. There IS a civil war going on in the party, and the moderates won. Hence we have Mitt. But the base of the current GOP is something different. The 90's were okay, unless you liked recreational drugs.
Given the choice between Clinton and Romney, I would vote for Clinton any day of the week and twice on Sunday (at Democrat run polling stations, of course). The problem is, Obama is not Clinton.
As far as policy goes, Obama and Clinton are much more alike than not. Therefore, your statement about choosing one over Romney but not the other doesn't hold water. Which in turn means that your distaste towards Obama is more visceral than logical.