We are now living in an age which is built on self promotion.
I don't like it, but it is a fact that many celebs nowadays give themselves a catchy name, do a little self promotion and next thing you know they are somehow or other hits.
Our President is well aware that the population who responds to self -promoters CAN VOTE TOO.
What you perceive as childish ranting is actually directed to that audience.
People of substance recognize what he is doing and accomplishing and do not need in-your-face bragging about it.
P.S. Look at all the celebrating and self promoting athletes do after EVERY play.