I don't know what your experience is but I feel quite confident in saying the 1st type is mainly discourteous arseholes who genuinely don't give enough of a shit about you to respond. For things that matter, it's not a politeness issue, it's a human decency issue.

As for people getting offended, people get offended for all sorts of things. In that specific instance, you can tell them if they expect that you know them well enough to not assume they forgot, they ought to know you well enough to reply indicating they'll answer properly later. If that feels to combative you could say kindly RSVP. It'd feel like youtubers saying like and subscribe, but at least it'd i crease their chance of formulating some immediate response.