This is "fairly simple"
While Harden may want the Clippers he certainly can't force the issue and the 76ers do want a realistic return for Harden that I'm not sure the Clippers can piece together (especially without including Mann).
The Pelicans do need a healthy Zion and while CJ McCollum has done his job providing offense he's also not a top-notch offensive ball distributor quite the same way Harden is. The Pelicans also have to be , if they are smart, wondering how effective McCollum is going to be at the tail end of that current 3 year deal.
Moving Harden for McCollum gives the 76ers a nice complimentary piece , plus the Pells may well be able to keep Harden once his deal is done assuming a healthy Zion it's a much better team.
The Wizards essentially swap Delon Wright out along with a 2nd round pick in 2024 to get a 1st round pick in the same draft.