I think there should be some incentive for that, like make those kinds of comments a spotlight or something. Maybe make a community called “late replies” that showcases the best such replies, or have a rule saying they grant free karma (in Reddit’s case).
Every once in a blue moon, I’ll skim over my saved posts and comments. Even more rare, occasionally I might respond months later if I think I apparently forgot to respond when the thread was fresh.
Just a couple or few days ago I responded to a comment from like 6 months ago where someone asked me for a link to a project of mine.
Regardless, that’s very rare, even for me.