Kessler syndrome doesn't "work" with the orbits these sats sit in. Even left dead and tumbling, the sats would re-enter by their own in ~5 years time. Even less with the recent lowering of their operational orbits.
Also, a common misunderstanding of orbital mechanics (probably amplified by otherwise great cinematography, but poor physics depictions movie Gravity) is that after a collision things move to higher orbits and thus remain up there forever / change planes and affect other satellites. But that's not how it works, the orbit gets elongated, but the periapsis remains the same (or slightly lower), so the things / parts / pieces still re-enter the atmosphere. And the satellites are grouped in rings, with different inclinations, making it extremely hard to reach one from the other.
Also also, space is like really really big. Plenty of space (hah) to put lots of rings of satellites and coordinate between themselves up there. The operators are the first ones who care about it, and they're slowly improving the existing systems, in both tracking (and access to tracking) and automated collision avoidance. Having 10k sats up there makes you good at keeping them separated.