An important reason for lack of adoption is simply because that every PC or laptop comes with Windows installed for free (as in gratis). People are generally lazy and don't bother with installing another OS. I'm pretty sure that the general public doesn't need the feature rich MS O365, and certainly doesn't care about the toxic community or GNOME vs KDE/Plasma. They just take what's already installed.
Three years ago I installed Linux Mint on my fathers laptop because of the slow performance of Windows and all the malware issues that he had. Before that he used to call me once a week the ask for help for his laptop but that stopped immediately after I installed Mint. He's a happy Linux user now but he can't tell you anything about his desktop environment, package manager or whether he's running systemd. He doesn't care about that, he just wants his laptop to work. If the laptop had come with Mint in the first place he probably wouldn't have known that it had Linux on it.