Baseball is a game of thin margins, and most execs got to where they are by piling up a bunch of 52/48 type victories.
The unfortunate side effect is they are, by and large, terrified of doing anything that isn't a slam dunk win. They NEED deadlines to act like adults and consummate deals. That's why more and more all the offseason activity happens around key dates as well (winter meetings, holiday break, nontender deadline, spring training reporting).