To give a slightly different answer, because they don't need to.

Intel has their own foundry, AMD is quite happy with whats a fairly recent move to 5 nm. Graphics card manufacturers are more concerned with selling off old cards than making new ones.

Apple isn't going to get very good yields out of 3nm and will likely only get to put it in a few products for now, but for a few months they get to say they'll be the biggest baddest company on the block, which is what apple marketing is all about.

Qualcomm gets the entire mobile market either way, and for desktop/server manufacturers apple isn't an option. Apple 3nm doesn't directly compete with amd/intel, so why worry