Good Marketing and Stupidity.
The stupidity was not that of users.
It was the stupidity of those many corporations that had significantly better computers than IBM compatibles (which was the 'default' name for PC back in the day), and significantly better operating systems than the various incarnations of MS-DOS.
So at a time when many of these corporations held huge market shares outside of the mainframe world, for some reason they just rolled over and played dead when Microsoft and IBM said they had the only computer and operating system you should take seriously.
Why should users shoulder the blame when almost no one they trusted argued that perhaps these other computers and operating systems weren't just "game computers" or "home computers", they were in fact more capable of running word processors, spreadsheets and databases than anything running MS-DOS or one of its many variants.
They were more reliable - which doesn't mean they didn't have viruses, didn't crash and didn't lose all your data - they just did it a lot less.
Computers capable of 3D rendering, fully capable of auto configuring hardware, had standardised video and sound chipsets, multi processors - capable of video editing, pre-emptive multitasking, and many of the things Windows only truly introduced in the last 5 years were available on computers in the 80s.. and cost no more than two colour, no sound, PCs.
I'll bet Microsoft were in fits of laughter and disbelief when the only answer they had for that "Yes but you can't take a computer like that seriously, it's only for games and hobbies" was swallowed whole by more or less everyone.
Then they had Intel - a company that managed to convince even people who should have known better, that megahertz was everything. Yes, yes I know they have multiple processors that share the load, operate more efficiently, produce the same result with half the required processing cycles of ours. But our processors are capable of running at 30% more processing cycles than theirs, so ours must be better.. Apparently we had a huge problem with math.
If it takes twice as long to produce the same result on the equivalent processor, why does giving the lesser processor 30% extra make it better? Wouldn't it need to be 100% faster to produce the same thing in the same time? Possibly, but only if you don't take into account that these other computers then shared the load between multiples of their more efficient technology.
Thus one computer could edit live video in real time, the other could update a database entry quite quickly.
The truly odd thing was that only a tiny fraction of the population wondered just how fast such a computer would be if you tied all it's resources to more mundane tasks.
But like I said, the problem was not the users - the problem was the corporations behind these computers decided to take all the bullshit lying down while they tried to figure out how to buy a corporate jet or whether their logo was big enough on the side of one of their buildings.
You want to know what the really crazy thing is? Why I said Good Marketing and Stupidity?
The same people that told us fancy graphics and all those processors where just for games and hobbies have managed to turn not only games and hobbies into the reason we buy computers - but that this is now more important than more mundane things, like reliability, security, efficiency.
If it wasn't so sad, if it wasn't the reason technical innovation was effectively held back 10-20 years, you'd have to say it was brilliant.