I love Rust, but I do not like how people are rust evangelists and look down on everything else. That is not how we in the Rust community look at things.

Now, with that out of the way. Andreas has been very clear about the reasons why C++ is the chosen language. He has years of experience with it along with writing browsers.

Im paraphrasing here, but he has said that the web evolved around the era of OOP and C++ is the OOP language of that era. Including statements on how C++ fits nicely with the OOP styles of web specs.