Some algorithm improvements ripgrep uses could be brought into grep, but ripgrep at its core just operates differently. It uses threads by default, assumes unicode, has a completely different regex engine, amongst other things. It could also probably be argued that some things from ripgrep would be pretty difficult to port from Rust to C or C++ safely.

burntsushi has a blog post on it here: https://blog.burntsushi.net/ripgrep/