Isn't it the curvature of the fretboard (to allow for bowing individual strings) that prevents chords on a violin rather than lack of frets?

Chords can be rolled. Here's an all time favorite

https://www.youtube.com/watch?v=ngjEVKxQCWs&list=RDngjEVKxQC...

I can play chords on a violin or viola and strum them. Keeping a four-finger chord perfectly in tune in rapid changes is really hard (near impossible) without frets.