If Microsoft were deleting Firefox, there would be a outcry and companies would fight back. My guess is that Netscape is vulnerable because of its age and its orphan status. Windows is able to search out programs that aren’t up to Microsoft’s current standards and define those programs as “defective” and premptively delete them.
Keep in mind this may have been an old program but it’s been working fine for years. I use it because it works and it has features I like and I’m used to it - and because it’s my choice to make. It was after all IE that stopped working not my old Netscape program.
To use the car analogy, I’m driving an old car but it runs okay and I’m happy with it. Maybe a new car would have a GPS unit and a MP3 player but that doesn’t mean my car is broken because it lacks those things. So I don’t want some car salesman to tow away my car in the middle of the night because they decided it needed maintenance. And then claim that the best way to “fix” my problem would be to buy a car from them instead because they’ve already put my car in the crusher.