> why can’t they increase the orbital radius to solve this problem?

Because there isn't a problem. LEO contains more than 200x the volume of commercial airspace.

We run out of spectrum and launch capacity well before Kessler cascades become a problem.

The reason starlink are so low in the first place is its cheaper to launch to that altitude, you need way less signal strength for devices to connect to them and the round-trip latency is vastly improved. They're intended to be essentially disposable, they're going for shorter lifetime and iterating on hardware improvements faster.

The further out you get, there's less atmospheric drag and each satellite is in view of the ground stations for longer but the cost of launch is higher and latency becomes a big issue. People expect 50ms latency for internet access not 500ms.

WP says Low Earth Orbit is popular because it's cheap to get stuff there, the latency is low (speed of light starts to matter when you're a couple Earth diameters up) and bandwidth to the ground is high (I assume it's harder to send a signal a longer distance, even through vacuum)

https://en.wikipedia.org/wiki/Low_Earth_orbit see "Use"

Automatic EOL (end of life) deorbiting is a feature not a bug.

I will again note that if Saber Tooth tigers had put things in the orbits we have, it would still be our problem.

very simple explanation but there's a few issues

radio bandwidth: higher frequencies travel a shorter distance and provide more bandwidth. so you get frequency contention and also you need your sats to be physically closer

latency: the further a sat is, the higher the latency. not an issue for text messages. a huge issue for phone calls and general internet tasks. the further you "push" your sat "back", the worst the user experience is

there's other issues too, like geostationary vs geosynchronous and coverage and exposure.

Low orbit is how star link is able to achieve their connections, isn't it? I think of they moved to normal telecom orbit the performance would be like normal satellite internet too

Not with a geostationary orbit. That must have a fixed radius. The problem is that satellites have to move to counteract the force of gravity to avoid falling out of orbit. But if they move too much or too little, then the satellite moves with respect to the earth and the orbit is no longer geostationary.

(Caveat: Not an expert by any means, just someone who had a similar question and did some reading, so my answer may well be incomplete or not fully correct.)