Why? He has 1 more year of control, is significantly cheaper, almost 3 years younger and has far more positional versatility. All this while showing improvement every single year offensively. I guess it comes down to whether people think he's a plus defender at SS/2B or not.JBJ is worth much more than Baez.
JBJ may be worth more, but I doubt it is "much more." Even if you think JBJ is a 4-5 win player, Baez has the offensive and defensive potential to match that. This is a kid who hit 36 HRs as a 20 year old between A and AA, from the SS/2b position. The power is legit and he's just now entering his age 25 season. He's younger than Betts and Bogaerts by 2 months.
He's not an OBP guy, but I could easily see Baez putting together some .270/.320/.500 type seasons while playing above average defense at either 2b, SS or even 3b. He could replace Pedroia if need be, allow you to trade Xander or move Devers to 1b. I'd have to think long and hard about a JBJ for Baez swap. I think people are being far, far too dismissive towards Baez but this board has a somewhat negative view on low obp/high slugging players.