In my day that’s just how it worked.
When my new principal came in 2019, one of the first things that she made clear was that she would not tolerate the use of "that's how we have always done it" as a reason (or an excuse) for doing anything. Any proposal has to stand on its own merits, and you need to be able to justify why you feel that is the best course of action to take (one way was to do up a comparison table and weigh the pros and cons respectively). Just because that's how our predecessors had done something in the past doesn't mean that was the best way then, or that it continues to be the best way today, or that there were no problems or tradeoffs whatsoever.
As I stated above, the consequence of people being able to freely download software from the internet was the proliferation of malware. And users would come to manage this issue not by educating themselves, but simply by downloading less software than they otherwise would.
I honestly don't know if the situation is any better on macOS.
Compare this with the state of iOS, where Apple has managed to get users to trust the download process, which in turn led to more apps being downloaded as a result, and developers benefit from making money than they otherwise would have (iOS generates more money compared to Android despite having fewer users). Incidence of malware also appears to be less compared to Android, where one of the main attack vectors is, predictably enough, via sideloading.
I do recognise that this line of reasoning can also be used to argue against Apple's 30% cut, just that I haven't really seen anyone argue convincingly for why 30% is too much (besides "it just is"), or what a reasonable cut might look like (besides "make it zero and let Apple subsidise the costs of operating the App Store via iPhone profits).
I also feel that it is the lightness of mobile platforms like iOS that allow PCs to be "heavy". I can accept that PCs could and should stay open, given the nature of tasks that people perform on them. Meanwhile, iOS should remain closed, again, given the. nature of tasks that people perform on them (eg: they use banking apps on smartphones but log in to a bank's portal via a browser on computers). They don't necessarily need to mirror each other (too closely), and perhaps they simply shouldn't.
It's kind like how I own both a MBA and an iPad, and I am happy with my MBA running macOS and my iPad running iOS (rather than both running macOS). I do my lesson prep on my Mac, and my iPad displays those resources in the classroom. Each has its own strengths that allow it to stand out in the right conditions, and I have no desire for them to essentially be a carbon copy of the other. 😬