Jake Mangum (Miss State) was a fourth round pick after senior year. He signed for 20K. Slot was 487K. His options were sign or go home. The word is several teams contacted him the previous year offering 300K if he would sign. He wanted to return for senior year as 23yo to win the CWS.
There isn’t a personal baseball future reason to return senior year unless the player believes he will go from undrafted to drafted. All the leverage is gone.
You’re also one year older waiting until after senior year. If you’re in AA at twenty-six for reasons other than rehab the Grim Reaper isn’t far behind (unless your name is Tebow).