For sure that is a factor. But baseball has some incentive. The younger a player can help the ML team the longer they can help the team. Is that not an incentive? Perhaps not as strong as the service time/cost issue.
You only control a player for 6 years, so a player helps the team for the same amount of time no matter his call-up age. What you don't want to do is to waste any of those 6 years while the player isn't really ready to contribute.