I wonder of they will ever invite juniors who leave early to these All Star games? Especially 4th year players.

The #1 overall pick in the draft usually doesn't play in the Senior Bowl

No chance.

The NCAA promotes players getting their college degree. These All-Star games are designed to reward players that have completed their eligibility but
perhaps didn't get to showcase their skills in front of more scouts whereas underclassmen have extra year(s) to do so.

However I don't think the NCAA has anything to do with these games.