Why did the can crusher quit his job?

Q: Why did the can crusher quit his job?
A: It was soda pressing.

This is another pun. The pun is on the fact that saying "soda pressing" sounds like "so depressing" when you say depressing like "dapressing" (which many Americans do).

Since a can could reasonably hold soda, and to crush something requires applying pressure to it, the first sense of the pun works.

Having a job where you crush cans all day might be depressing to people that like more intellectual stimulation than that, so the other sense of the pun works as well.

Why someone would hire a can crusher is an open question, however the idea seems a bit absurd.