There is zero reason, ever, to sign a long-term deal with a player in their pre-arbitration years.
They're already locked in for cheap. The only pros are that you might save some money if they don't regress or get injured., and that you build some goodwill with the player.
The billionaire owners can afford spending a little more on a proven commodity and there are other ways to keep players happy. Plus, I can only assume many players who lock into these deals regret them years later when they see their market value rise. So it's no guarantee of happiness (if there is such a thing, haha). One could argue that these deals might increase strife. It's pretty common for a player to be upset when a team changes course, rebuilds, hires a new front office, etc, and then they demand a trade or drag others down with them.