It's the same question I ask why people are still using Windows for their Desktop. Like, is this even still a thing even while much better alternatives like Linux are available? Using Windows for your daily business laptop/pc? It's like sending post cards with your data. But it's to each their own, I guess.
Skype doesnt have native Linux support and the propriety version available has insane privacy concerns, like recording the mic in the background and recording all keystroke inputs, regardless if not in chat window and so on. Telegram is probably doing similar stuff, but much less as it's code can be verified and is.