I personally get why this would be frustrating, but in my rules I said I'm not forcing someone to put a message. I only say it's mandatory with suggestions for fairly obvious reasonings (aka I'm not a mind reader).
I've become aware (mostly due to people's signatures) that social anxiety is a thing, even when online. I myself just say the same message every time I send offers; "I hope this is okay. If not, I get it." I say this not to be generic or repetitive, that's just my mindset. If you don't like my offer, it sucks, but okay. If you say it's okay, that's okay, too. I almost never send open offers though unless it's offsite trades. I always send an offer I know the person was asking for. Even then, they still sometimes cancel.
Another thing is I can definitely see newer users being intimidated with older users. I remember when I was a younger user (not on CS) and another, much older user talked to me, I wouldn't talk back because, frankly, I was scared of them. You don't wanna look like an idiot to an older user, even if you literally joined five minutes ago. I know this was when I was a literal kid (again, not on CS) and, while I'm not saying this is still a thing, I can see it being a thing. Not many older users (2012 and older) are still kicking it in the forums. I almost exclusively stay in trades areas with occasional comments elsewhere, so I know I see more like 2017 and younger. If being intimidated by account age is a thing, you sure as stuffing won't talk to me if you had the chance to talk to, say, someone from 2020. And this doesn't factor in people who come off as intimidating. I know I can sound like a massive jerk, even when I'm not!
I know this is an annoying thing, even I used to be annoyed with it, but it's not exclusively from laziness. There's so many factors that could play into this that I just stopped caring, basically. Consider it a bit of a water under the bridge kind of thing.