The difference is that neither your 1979 Apple 2 or your Win 3.1 machine are connected to the Internet.
I used to use epidemiology analogies to explain this issue, but if 2020 has taught me nothing, it's that we don't have a universal grasp on those concepts.
When viewed individually, disabling Flash Player is annoying. When you view it in the context of the larger ecosystem, disabling by default it is a no-brainer.
Flash Player is one of the few pieces of software on your computer that's tasked with processing fundamentally untrusted content.
The biggest problem anyone had to worry about in 1979 was Tom Cruise Matthew Broderick and a 120bps modem with an Acoustic Coupler hooked to a rotary phone. In 2020, we have thousands of experts working diligently for both state-sponsored agencies and organized crime, creating and deploying malware for various reasons. That work product includes a global infrastructure for detecting vulnerabilities, exploiting them, and deploying malware en masse for various economic and strategic ends.
Because we're primarily tasked with processing fundamentally untrusted content, much of the work that we do on Flash Player is about keeping up with the latest academic security research and intelligence about what attackers do in the field. Security is not static, and we're continually improving our security stance. That work has stopped, and at some point, that automatic vulnerability and exploitation infrastructure will catch up. Again, when viewed as an individual, having your identity stolen (or having a missile lobbed in your general direction) is a personal tragedy, but when viewed across the billions of existing installations, disabling Flash by default is necessary for the health of the Internet at large.
In that vein, it's not just Adobe removing Flash that's in play. All of the major browser vendors are removing support for browser plug-ins across the board. Even if you had a working Flash Player, you'll be hard-pressed to find a browser that will continue to run it.
We do have some mechanisms available for enterprise users and archivalists, but we expect those people to have the expertise and resources necessary to secure those installations. Long-term technology archival is a huge and complex topic, but there are well-known industry methodologies available for creating and running legacy operating systems and software on modern hardware in a way that's both secure and viable long-term.
Those topics are well beyond the scope of what we're going to advise on here, and well beyond the capability of the average non-techincal user.
The bottom line is that your camera vendor has had three years to produce an update to resolve the dependency on Flash Player. Assuming that your cameras or DVR have the ability to take software updates, the decision to either produce or not produce an update to remove Flash dependencies (this is totally doable) is theirs. It's possible that there's a firmware update already available. It's definitely worth reaching out to their support people about.
https://theblog.adobe.com/adobe-flash-update/
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