Time per Move

Why doesn't Chess.com (the wonderful site it is) not have 2 or 4 days per move.?  Is there a reason for this or is it just the way it is. Im not a fan of games going on and on but sometimes you cant be online all the time or everyday so a 2 day option would be handy to a lot of people who enjoy a fast game but have got less of a chance of timing ou.