There are plenty of reasons why trading for Jalen Duren could end up being a huge mistake for the Bucks, but the biggest might be that he doesn't have the right skill set that Milwaukee needs most. More than anything, the Bucks are lacking a solid point guard amongst their young core, and obviously, Duren doesn't fill that need in the least.
The Bucks do have plenty of promising young guards, but most profile better as shooting guards or combo guards than true floor generals. Considering the importance of strong point guard play in today's NBA, the Bucks' main focus right now should probably be improving their future talent at that position rather than adding a center, which is arguably the least valuable position in today's league.
A point guard improvement should be the Bucks' top priority
Probably the Bucks' best bet at a natural playmaker and floor general is Kasparas Jakucionis, who came over in the trade package for Giannis Antetokounmpo this summer. But calling Jakucionis unproven in the NBA would be an understatement. He's coming off a rookie season in which he played 53 games and averaged 6.2 points with 2.6 assists per game. Not exactly the numbers that make you feel confident about your future floor general.
Last season, the Bucks relied on Ryan Rollins as their point guard. And Rollins performed admirably, with tremendous growth from the previous season. His progression has made him a very valued member of the Bucks' young core now, but it's still clear he would thrive more with a better playmaker next to him.
Rollins is at his best when he can play a combo role as a secondary playmaker and focus instead on his individual scoring. He's got the size and shooting to line up as a great shooting guard for years to come, but the Bucks will need better playmaking throughout the roster if he's their primary ball handler.
Duren is demanding money that only makes sense for a point guard
The reason the Bucks need a point guard so badly is to uplift the entire offense. A great floor general should be able to set up his teammates and get everyone open shots. Duren had a great scoring season last year, but he did little to help his teammates get better looks.
Adding him to the Bucks now wouldn't necessarily make life easier for the other members of Milwaukee's roster. It might help the young guards have a lob threat, but Duren won't be making plays for them in the same way that a point guard would. And considering his contract demands (north of $40 million per season), Duren would need to serve as a proper offensive engine to be worth the money for the Bucks.
