There is a disproportionate amount of LEO satellites in polar orbits. Particularly morning time sun-synchronous polar orbits.

If everything in that orbit (the most crowded one) starts kessler syndroming it up, I think all the junk would mostly stay in polar orbits?

Can any orbital dynamics experts confirm? I was kind of just adjacent to that area in a job previously.

Probably? I don't think masscons are big enough of an influence, but what timescales are you talking about?

The Starlink satellites have a design lifespan of about 5 years and will reenter the atmosphere relatively quickly even if not actively maneuvering, simply by virtue of being so close to Earth.