People text instead of calling and especially instead of leaving voicemail. Just asking one question seems rude via phone so the conversation is buffered with "hi, what's going on, how's the weather, how about them lakers, while I have you, what do you think about this, etc."

Phone calls are less information dense to many developers to something like slack, especially if you need to send a link, a document, etc.

Slack is also async in that I don't have to immediately answer. I can get to a nice commit point in 5 or so minutes and not have to stop in the middle of a deep thought.

If it's a scheduled call once a week though, that shouldn't matter at all. Maybe they just don't like you :D j/k. A lot of devs think they communicate as well via voice