More modern systems are also down once in a while. With aviation it's just more visible because one system can affect a lot of people.
I'm not sure when ATC systems (which I would count NOTAM to be one of) have last failed, I always had the feeling they're very stable. It's usually airlines that struggle with their applications.
I never know how well it applies but headline outages always make me think of that “The Coming Software Apocalypse” Atlantic article from a few years back[0]
All hyper optimized systems become fragile until they collapse.
The NOTAM system is ridiculous, no surprise it collapsed ... you can lose your ticket for flying thru a MOA that went active AFTER you took off.
What could possibly go wrong with a "push" notification system for every tiny little detail of aerospace scheduling?
No force is as destructive as the good idea fairy.
I'm not sure your specific example is a particularly good one. I can legally fly through an MOA that's active, without needing ATC or military authorization.
That's the curse of niche software. Especially one made to fit, it's easy for penny pincher to decide "it works fine now, it doesn't need ongoing improvements" and you end up with some ancient shit needing java 1.7 (or worse) to run with no plan to upgrade.
The software is tied to a dependency chain of real people (passengers, crew, etc), real equipment, and lots of constraints. So problems have a downstream effect that's more pronounced and visible than many other spaces.
It feels like not a single month can pass these days without some "Airline X has major outage and ruins tons of people's days!" story on the news.
What is the tech behind these frail systems?