5000 is one hundred victories. You are not getting more than one victory every five minutes (especially when you calculate the time it takes to get a match, the load screen when that happens, the match itself, and the upload/win screen). Even if you are a brilliant player, and you don't lose a match, and you play without breaks, it will still take you close to eight and a half hours to get those points.
Now, that is an ideal, and quite honestly, silly scenario. You can double that time, as you are not going to be getting matched instantly (so there will be more time in between matches), and you aren't going to win every match. So, more realistically we are looking at around seventeen hours.
Most people aren't going to play seventeen hours in a week. Only the hardcore will get close to that (and many of them will have too many responsibilities to put in that much time, even if they want to). It would take weeks for some people to get that one character. So, that seems like a more than reasonable estimate.
Now, I think they could MAYBE get away with as high as 10,000, but they would undoubtedly receive criticism for that move. Probably much more than they would want.
Capcom is looking to create return interest, to keep people coming back, to keep people buying the aesthetic stuff that requires real money. If they make the cost of a character too expensive they will discourage that return visit.