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).
I haven’t recently, but when I am trying to solve a problem and come across a post/comment which does a great job of helping me out, I’ll sometimes post a “thank you” to the author. On the receiving end of things, I had posted a couple of kinda useful scripts in the PowerShell sub-reddit and would get both “thank yous” and questions regarding those scripts from time to time. I also had a really popular post (it’s still linked in the wiki) in the cordcutters sub-reddit which elicited questions years later.
Otherwise, this experience is far more common.