In-universe, commanding officers seem to have the authority to decide which uniforms the crew will wear. Janeway liked the jumpsuits, therefore the jumpsuits were the preferred uniform for all.
In DS9, when Sisko becomes temporary head of Starfleet Security on Earth, he wears the TNG-era uniform. It seems to be a more formal uniform, between the dress uniform and the "fatigues" of DS9. Would make sense for Picard to prefer a more formal uniform for his starship.
Don't forget the in Generations we saw Troi and Worfwearing a TNG uniform when she crashed the ship, but Riker and Data were in the DS9 uniforms in the same scene. So it might've been more a transitory phase.
Or they just decided to wear the DS9 uniforms that day, I mean Picard was wearing a DS9 uniform during the later parts of the film and then switched back to the TNG Uniform for the very end of it.