99 percent invisible just did an excellent episode on those phones and why they were indestructible.

TL;DR the phone company owned them and had to pay for replacement and repairs.

https://99percentinvisible.org/episode/100-objects-019-western-electric-500-series/

They can. They do. You can buy them.

Then most people say "I'm not paying that for a lead, I can get five normal ones for that price!"

I used to munch on stringy phone cord as a kid. Parents thought it was rats but no, it was... it was me.

I... don't hate it.

If you take a thin lead and wrap it round a pencil the use a hair dryer on it then it becomes a curly lead .....

bought something vaguely like that for my keyboard

https://epomaker.com/products/epomaker-mix-pro-cable