Some only find privacy in their bathroom you know
Technically, you don't use PC to install .apk on phone, you download the file then copy it onto your phone and install it there, you use PC for better download speed and utility.
People who has problems with installing/downloading either their device using older android version, the file didn't patch correctly, their device is out of storage, old ver messing with the new one (try uninstall the old ver) or download site like Mega limits their download. (5GB daily for free user)