"Any complaining about the unfairness of the debate is an admission that Trump failed in the negotiations for the debate rules or in his preparation for the debate."

Or....
Trump needs enemies to fight. His base loves to rail against the enemies with him. It's the WWE wrestling format without the costumes. Winning by losing.

Knowing he could not do well in a formal debate, before accepting an invitation Trump & Co. planned a strategy to fail and capitalize on that failure.

That plan includes accepting terms and conditions he could rail against, and moderators he could lambaste as corrupt media.

Trump sees the loss as an opportunity to further enrage MAGA, launching a new product, another round of fundraising.

His team has already scripted the ads, teleprompter dialogues, etc to maximally capitalize on the planned loss.

"We were treated so unfairly, we need to show them that the American people will not give up without a fight!... send me mo-money."