BUT, there is precedent for this move. They gifted an even more expensive plane to Erdogan. From what i understand they have been trying to sell the plane for a while. It seems even they have trouble affording it's upkeep. Turns out there isn't a huge market for luxury private jumbo jets. From their perspective it's a white elephant. Trump is aware of that.

I heard another explanation that this is a way of putting lateral pressure on boeing. Trump is frustrated with the progress of the new air force one. His current one is aging. It makes sense as it's a typical tactic of his.

I'm not coming to defend it, just to explain some of the rationale behind the decision.

(edit to reply to several comments. First of all air force one is well maintained but it's old already. Parts and repairs become more difficult and the amount of miles left on the airframe can't be too high. Replacement is necessary. As to building a new plane out of spares being faster... Just ask boeing how that's going for them. They even had the fuselages ready and waiting for quite some time. Boeing executives know they will face some actual consequences for murdering the POTUS, which is probably why it's taking so long. It's difficult to build a plane properly when you've gotten rid of everyone who knows how and you've sold half of your factories, some to even more bad faith actors then yourself.)