A couple things: your fonts render better, your text is in Unicode (may not be a big deal for Americans, just trust me that I care that I can write reliably in

A couple things: your fonts render better, your text is in Unicode (may not be a big deal for Americans, just trust me that I care that I can write reliably in my own language), your kernel has to support many more abstractions. But the real issue is that the browser does a lot more than it used to and languages with JIT compilers and automatic memory management are just going to have a much higher overhead than C++. This is doubly true when the languages are non-typed and ultra-dynamic like JS. For a while I browsed the internet without JS enabled and sites that didn't break loaded without any visible delay.