Why are they so cheap?

Pretty much this. They are pretty good cars overall but the ones being sold are generally in need of overdue maintenance which is going to add several thousand to the price. Bearings, bushings, springs, hoses, shocks, belts, timing chain, tires, and so on. Then just when you think you're good to go, you run into a bunch of other meme issues like your alternator shitting the bed, thermostat shitting the bed, or water pump shitting the bed.

I used to be one of the biggest "just buy an old jap car, they are fine" shills but after having experienced the meme firsthand, I now see why newer is truly better.

can the same be said for 370z?

There were more BMW's & Z's at CLN then 240's
That said, after the inlet from my turbo manifold blew apart I went for a ride along in this Z that had only like $6k put into it, & it was fucking amazing in comparison to a 240. Just the stability & reliability, you honesty couldn't get a 240 at that state for the same budget.