As a comparison point, take a look at firewall options on a smartphone vs a desktop OS - I think you will find that the desktop has much more fine-grained firewall options (excluding root firewall apps on android), allowing you to specify which executable has access to communications on which ports and on what networks, whereas it's nearly impossible to block internet access to a phone app (since they all want ads of some sort via internet to make money it seems)
Look at muting an application - how easy is it to mute a single application in windows vs on a mobile device - can you specifically mute all sounds? easy to do in both - but what about program/app X? or can you adjust the volume of program Y such that it's half that of program X? I would say the desktop has more fine-grained access here
PC's also have more advanced monitoring options - you can go and see exactly which process is accessing which files at any given time, look at the individual threads for each process, run them through an anti-virus (sandboxed?), which while technically possible on a mobile phone is much less practical, and the phone-based AV's aren't quite as good as their desktop counterparts.
I think the overall reason is that a phone isn't really "yours" until you root it/gain admin access, whereas on a PC, that's the norm - as such, the phones want to compensate by making you "feel" empowered, even though you really aren't, whereas the PC can get you virtually anything you want if you simply configure it as such (run untrusted apps in a VM, sandboxie, etc.)
There also seems to be some usage differences, where on a phone just about every app wants access to your contacts, your location, etc. - on a PC, very few (if any) will ask to "sync" contacts across different apps, or even bookmarks - it's usually a 1-time "migrate settings" if anything - the apps are all very self-contained, as opposed to each app relying heavily on the system and other apps to do stuff for them (how many apps function in android without Google play services? what about on windows without service X running)? Look at media players - most desktop media players are self-contained in that they have their own codecs, whereas it's virtually impossible to find a media player that has its own codecs and does not rely on the system's codecs (and thus inherit its flaws) on mobile.