There are many layers to this if you think about it. They may try to save effort by only typing the question in case you are there. But also, it's a way to avoid you not answering. I mean, they may (perhaps subconsciously) fear that you will read the question and decide to procrastinate on answering it because it looks too hard somehow. Instead, if they get you on the hook in synchronous communication, it will be harder for you to "snooze" on the question. I mean you can explicitly tell them you'll take a look later but you can't pretend that you haven't read it yet. Or some may use it as an excuse to pause working.

That plus a lot of other mind games. In a way it's a power game, whose time is more valued, who gets to demand attention right now etc., who has more flexibility and convenience...

Also, sometimes when people are confused, they sort of emotionally panic and just need someone beside them, to hold their hand and comfort them virtually. Then if you don't respond, they somehow do manage to solve their problem on their own anyway. But it felt simpler to just interrupt your work and ask you instead of thinking or searching in the internal docs etc.

'Maybe' and 'it depends', are good intermediate remarks while painting the picture about the real question at hand.

Typical scenario though is that then they move on ask somewhere else. So they have to type it out anyway. If you don't reply, they can copy-and-paste the question to somebody else.

In the "which one of them do you like" domain... https://no-hello.com

Though there's also https://nohello.club