prozac0197
The first answer that I have is that it's an accessibility reason. All the technologies that you have mentioned are accessible. Everybody can learn, integrate, and implement and most importantly, they are fast to deploy. I think that it's also a universal language that everybody can speak. If all of a sudden everybody changes the tech stack, everybody will have just to learn a new paradigm to create websites.
Another thing that I might even consider (but this is something that is very much vague even to talk about), but I want to throw it out. I think there is a certain pride in creating so much code that it's still used even to this day, so replacing it is like saying that all my lifetime work just vanishes away. As I said before, this can actually not be the case. In the end, we are talking about things that are mostly static.