If you put the player as a starter, sub and a benchman at a certain position, he'll get 43 minutes and not 36.
The point is that if 48 min/walkover is allowed, teams will guarantee 48 mins by dealing a WO against a team that does not care of training. On the other hand, teams that actually play a scrimmage will risk not to complete this quota by fouling out, being tired or if not lucky, getting injured. So from the perspective of the developers, I see they tried to make a ballance between those 2 issues, and I think 43 guaranteed minutes without any risk are quite within the ballance of 48 minutes having such a one. Maybe 44 or 45 is even better choice, but it's really not a big deal.