Universities were already locking down their PCs in the 90’s, at least those with competent IT departments - BIOS password, locked boot menu, Windows 2000 with restricted user accounts.

You need to make up your mind on what time period you're trying to use. 90s? 2000? Before you were talking about Windows 95.

But notice, you're talking about universities: we're talking about children under 18. Those computers were not as locked down. That has changed from the 90s. The security of the 90s (especially before TCP/IP was standard) was different than 2000-2010 security, which was different than 2010s+ security. Yet, you're trying to claim it hasn't changed? That's so inaccurate it's laughable.

Even in the Linux world, Pre-IP vs Slow Internet vs Fast Internet vs Post-sudo security models have changed a lot. I'd be skeptical of anyone trying to argue that the security and lockdown of these computers has not changed in 30 years. Is that your argument? If not, why did you start with "Windows 95?"

If you don’t do that, your every PC will have 15 copies of Counter Strike and a bunch of viruses in one week.

And? People still get viruses. People still install games if they can. The tools to do that on PCs are far better at trying to stop those than 30, 20, or even 10 years ago. Chromebooks are even more effective than those tools at locking them down to be unusable.

Chromebooks (and laptops in general) are way cheaper now than PCs were back then, so again, you need to buy your own and install a proper OS, the situation did not really change.

Before: if you wanted to do work at home, you or your family had to buy a computer. Kids (might) need to convince their parents to do experiments, but it was far easier to do that to convince a school administration.

Today? What families have a "family computer?"

Kids get a phone, they might get a tablet, and if they get a computer, its the school one. The need for a family computer has basically gone. All of the computers are locked down. Google happens to make locked down OSes for their replacements: Chromebooks, Phones, and Tablets. Yet, according to you, the requirements hasn't changed. Yet, from a child's perspective: they'll probably never get the opportunity to play with a non-locked down computer.