I don't like it either. I find (generalising but true in my case) it's mainly older or senior staff who ring straight up, and younger staff message first / schedule a call for later (like on phones).
Truthfully, I also often sit on the sofa with my laptop (I know I know...) but prefer to look more 'professional' on a call by hopping to the table next door. So I want the opportunity to say 'yes fine', then just up myself across, which takes marginally more time than someone typically holds on ringing for.
And very occasionally I'm still in my PJs and want to grab a jumper to put over me. So, yep, there's that too. Which isn't a good reason, but a truthful one!
But, most of the time, the reason I don't like it is because I am available, but I would find it better to be asked 'are you free for a call?', me reply 'yep give me 3 mins to finish this email and Ill call you', complete the task while you're in that headspace, then call. The DNB button does not work for this - I'm not really 'officially' uninterruptible doing something that needs 100% concentration, I just want to complete my work tasks in way where the email gets sent before the 15 minute call rather than after when it will only take 3 minutes more
Why do I care? For me, it's just being in control of my tasks. If I have in my head I'm doing one task, and get diverted to another by the unscheduled call, I find this more stressful than having it scheduled. It's only a little bit more stressful, I can cope - but I notice it. Everyone knows that 'running around doing a gazzilion things at once' is stressful. It's just a micro-version of that. Why have that stress at all if a little message can be sent?