The programs are very uniform. There is not multiple ways of doing things (at a presentation level). So you get to use hundreds of thousands of existing apps written over the last N decades in your modern web application.

You just couldn’t write them all over again, there isn’t a team on earth that could, even with infinite money. You’d be talking, I think, more than high double digits, millions of LOC.

JavaScript by comparison .. today it’s React/Angular, but it is very fluid. Not much code will be practically reusable in 5/yr from now.