I think it’s more a reflection that people mostly use other devices, like phones and tablets, for tasks they might have used a PC for 20 years ago - at least outside an office environment.

That’s not to say the PC experience hasn’t improved - certainly Windows is at least more secure - but that it’s not the only factor, and I don’t think it’s the biggest factor either.

One data point for you: the last company I worked for, when I joined in 2017, already >50% of external users were accessing our service via mobile devices.