So, to summarize:

1. Shove = 5ft. That's what makes Pushing Attack for Fighters and Eldritch Blast with special trait to push others special... they can shove farther as special abilities and magic.

2. Shove = Knock Prone automatically as well. Thus, making it so melee attackers gain advantage on prone targets. Thus, strategy. Thus, it is worth it to shove.

3. Shove = Action. It is an attack. It is not some minor extra ability. If Shove is a Bonus, one still does not need Disengage. I can shove an enemy 30 feet away and then shoot them or run to high ground or whatever. Why waste an Action to disengage if I can shove and still move and shoot?