It depends on how much of a browser you want to implement I guess. Comparing it with a compiler is a skewed comparison I think; compilers are built as part of many people's college/university education, but are only a small part of turning programming language into working software. Likewise, I'm sure most developers on here could feasibly write a web browser that can fetch websites and render the HTML.
But that's just one aspect, next you need to add support for CSS [1] and Javascript [2], each of which has had lifetimes of work invested in the standards and implementations.
So yeah, while it's doable to build a new browser, if you want to build a big one that has feature parity or is on-par with the existing browser landscape, you need a large team and many years of work. And that's just the practical aspect, the other one is, would a new browser actually be better? Could it compete with the existing market? So many players have just given up over time.
But that's just one aspect, next you need to add support for CSS [1] and Javascript [2], each of which has had lifetimes of work invested in the standards and implementations.
So yeah, while it's doable to build a new browser, if you want to build a big one that has feature parity or is on-par with the existing browser landscape, you need a large team and many years of work. And that's just the practical aspect, the other one is, would a new browser actually be better? Could it compete with the existing market? So many players have just given up over time.
[1] https://www.w3.org/TR/css-2022/
[2] https://262.ecma-international.org/13.0/