Because github does not offer the option to (and no, running github enterprise doesn't count).
They don't even let you really run those yourself now either, We moved off a big GHE footprint because the support for it was getting abysmal and features were slowly become GH.com. Ive been dreading the move to GitHub.com and it was worse than I expected.
So how's forgejo been going for you?
They couldn't handle sending webhooks for eight hours. That seems more than reasonable to expect.