His chief advisors are his kids, he has about enough staff to man a 24-hour fast food joint, otherwise its a one-man stage show. This is not a real campaign, it's all pretend.
It's probably not "pretend" -- as unsuitable a candidate as he is, Trump has nevertheless expended a significant amount of personal energy on this, and one doesn't do that in service of a pretense.
No, I think instead it's just the way he does things in his business life, and he probably thinks this is just another business venture. Unfortunately, his business dealings are all rather self-contained. He can flit from one to the next without strings, and his personal qualities play well in that arena.
Unfortunately for Trump, he doesn't understand that a national political campaign is strikingly similar to a large military campaign, in the sense of requiring long logistics chains, a ruinous tempo, and the need for people on the spot to translate strategy into tactics and results.