As things stand, mobile OSes have some pretty decent out-of-box ways for apps to be isolated. App A can't fiddle with data private to app B. That Android video game you just downloaded can't extract data from your web browser or generally fiddle with it.
Desktop OSes today don't normally have software install and work like that. Yeah, you can manually set something like that up with containers or VMs, but your typical user isn't going to do that.