Why is my personal hotspot button not showing

Probably an issue with your service plan or carrier. Personal Hotspot is a carrier feature, the carrier must supported and it must be provisioned on your account.

Contact your cellular service provider and verify everything is correct on their side.

Link-> If Personal Hotspot is not working on your iPhone or iPad (Wi-Fi + Cellular) - Apple Support

Because you must tap Cellular to find it. It is a cellular feature, and thus doesn’t appear at the top level menu in Settings.

If you don’t see it there, either than see Phil0124’s post above.

Actually "Personal Hotspot" should normally be at the top level in Settings as well as inside Cellular:

That's where I see it on all my iPhones.

You are correct; I missed that.