The term User for computer hardware and software customers has been universal for as long as I can remember. It has always applied to both hardware and software customers - There were "Lotus Users" and "WordPerfect Users", just as Commodore and Sinclair Users.
I struggle to think of other industries that refer to their customers as "Users", besides the computer technology industry.
It shouldn't be about technology. I don't recall CD and VCR producers calling their customers Users when those high-tech products were introduced, and I think the same applies to Nintendo and Atari (game consoles) too.
And it shouldn't be about things that are objectively tools. I have never heard of someone buying a hammer or drill referred to as a Craftsman or Dewalt User.
Other industries selling high-cost durable goods, such as automobiles, don't have Users either, though they often have "Owners". It seems to me that paying as much for a micro in the 1980's as a decent car cost should have qualified you as both a valued Customer and an Owner, so why a User?
Notably, the term does make perfect sense in 2020, where we have countless Facebook and Twitter Users who do not warrant being called Customers, since they pay no fees, and certainly are not the Owner of anything. So that actually fits - they simply Use.
There ought to be some objective history and reasoning behind the ubiquitous term User, instead of simply being called a customer, like in all other industries. From where did this demand to be called a User originate?
Update: If, as many suggest, the term User originated because it was an early and specific role, what did that role originally convey in terms of the person's competence, privileges, or restrictions regarding the machine? And does the same role definition thus roughly translate into similar expectations for a customer purchasing an early micro-computer for the home or office?