The primary point of hooks was to give function components the same capabilities that classes already had. In that respect, letting classes use hooks would have been superfluous.

At the same time, the React team _could_ have chosen to implement support for hooks in classes, but chose not to, both for simplicity and as a carrot to encourage folks to use function components where possible. Based on the discussions and examples I've seen, capabilities like Concurrent Mode and Fast Refresh work better with function components because there's fewer edge cases to worry about. While classes aren't going away in the foreseeable future, there's valid reasons to try to get the community to adopt function components more.