Same reason people are on LinkedIn, FB, etc. I don't switch because all the people in my call list are on Skype. Also, I don't have any smartphone, only PC and laptop, so I don't even know or care what kind of apps for iOS or Android there are. ON teh PC I have to use "Skype Classic", which MS would like to get rid of (default download is the app for Windows 10). That app is unusable, and I'm tempted to add "literally" for emphasis but I'll wait until this new meaning of this word is (even) more established and the original one more forgotten :-) For example, in the app I can't even control my online status unless I keep the app open, while old Desktop-Skype lets me choose the status and I can close the window but the service remains available through the taskbar icon. I'm also unable to see a list of my contacts filtered by who is online in the app, which I consider to be as basic as it gets.