Someone may run into some issues upgrading their one server, and decide to power through it. Enterprises create a project plan, have meetings, get QA involved, identify risks, mitigate them, need sign off from the security team, not just on the new Ubuntu version, but they may talk themselves into re-certifying the entire bla-di-blah. For them it makes economic sense (in the short term) to just pay for the support plan that keeps them "compliant" and comfortable on the current version.

And this, among other things, is why I like the agency that small companies should be able to offer you.