Why is there a limit of three years that a team can send players down to the minors without first having to put him on waivers, and having the player clear waivers? Why can't they send a player to the minors whenever they feel like it?
From my understanding of the options rule in baseball it works on 2 levels.
If you allow an MLB team to call up and send down players at will, there is no stopping them from using whoever they want, whenever they want, and it's basically a roster free for all. There are no rules, limitations, they could use all 90 of their players in one season if they felt like it.
For the players sake, it stops MLB teams from just calling them up when they need them, and sending them down when they don't. If there were no limits, or consequences, a player could be stuck in the minors for most of his contract if the team doesn't feel like they always need him, and it hurts his chances of really getting a shot, and working his career.