Windows has, before Windows 10, had a support cycle of 5 years for feature updates and another 5 for maintenance. XP was supported past that term for (too) long because people refused to or were unable to switch, and 7 has befallen a similar faith.
The news media recently found the support cycle page again after the leaks about the upcoming Windows 11 release, but none of this should be a surprise for people who need to look into long term support for Windows.
The difference here, or course, is that a big company like Microsoft is more likely to stick around than a small, open source project. They currently don't have any plans to stop support, but who knows what the future may bring. Covid is a stark reminder of how the world can change in just a few months.
I'm not sure that's a fair question to a new project. If you asked that recently about Windows 10, you'd have a different answer than today.
But seriously, Rocky was started by the person doing CentOS before and unhappy with changes. They're at the very least not planning to go away.