Maybe your tactics are all wonky? It's a management game, some still don't get that. You could have a team full of scouted players and lose to a team with lower, but hard earned stars, because that team is set up better. The orders/positioning/formation even the morale and fitness may be all-round better than your all-star squad - then they deserve the win. Why should it be better stars = always wins?? That would be a terrible idea, those with more money than sense would never lose in that case.