I hear people saying this a lot, and I admit I sometimes think it myself. But I'm not sure how true it is, as opposed to just a perception.
> Not even to the level that I, a curious teenager, had experienced in those years
I think therein lies the rub. Teenagers curious about computers aren't very common. And even back then (early 2000s), my experience in Europe was the same [0]. Most of the people in my school didn't really care about computers. They had other interests and pursuits.
The difference today is that computers are much more widespread because they allow people to do much more diverse things. At the time, they would maybe type up a report or something and that's it. There wasn't Facebook et al., so many people didn't spend any significant amount of time in front of the computer. Idle time would mostly be spent in front of the TV or hanging out with friends.
I think the reason this perception comes up is that at the time, people who "spent time on computers" were doing so out of curiosity and interest in learning about them. So the shortcut is that since now many more people are spending a good chunk of their day in front of the computer, that must mean they're as interested in them as the "curious teenagers" of our time. That's simply not true. Just look at what they do on the computer. It's mostly idle scrolling on some form of social media.
And, to address the subject of the OP, I'm also wondering whether there's an actual decline in the "general-purposeness" of the computer, as opposed to there just being more "non general-purpose" computers.
There's a definite decline in the percentage, and maybe even in absolute numbers if we look at people who used to use computers because they had no alternative but who are now better served by smartphones or tablets and also for uses which need "specialized processors" (say ML).
I draw a parallel to my feeling whenever I see discussions about iOS being locked down and people expecting the whole of the HN crowd to be up in arms about it. In my case, I was one of those curious teenagers of yore. I still love tinkering with computers, etc. But phones? I just can't be bothered to care about them. Can I make calls and check some maps? It's great!
I have an iPhone and treat it pretty much like a dishwasher. I barely have any apps installed. Neither allows me to install whatever random app I want. It's not an issue for my dishwasher, and frankly, nor is it for my iPhone. Whatever "general computing" I feel like doing, I prefer doing it on an actual computer.
Of course, there are other philosophical considerations in this discussion which I understand and can get behind, but the point is that, to many people, a computer is an appliance. They want it to do certain things. Does it do that? Great! If it doesn't, it's not fit for purpose. They simply do not care if some guy some where would like to do some thing with it but can't because Microsot / Apple are locking it down.
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[0] I went to school in the suburbs of Paris, so many of the kids' parents were pretty well-off and many were even working in computer-related fields, so there wasn't any access problem. Practically all of them actually had at least one up-to-date computer at home.