Not even close. Pretty much every enterprise uses it because, from an admin point of view, it does everything the customer wants. Centralised user management is pretty much mandatory for different compliance and AD and Okta meet those needs just fine.
Hell, from a user perspective, I don’t even hate the Okta SAML implementation now we have support for Yubikey enabled. Click a button, I’m in.
It's just a feeling seeing it mostly in banks and other old-school enterprises (AD plays a huge role here as you mentioned)