These can be issues for all sorts of people; age is just one potential factor, and no-one works well with too much clutter. May I suggest that all those unused macros are, for your current needs, clutter? File them away elsewhere.
Yes, “you can export macros and delete them and re-import them later if necessary”.
For keeping track of all those macros (or macro groups), just save them all into the same, clearly named folder (e.g. “Keyboard Maestro macro archive”).
Now you have just one folder to keep track of, and you can search it from the Finder.