Why would one want to replace nginx as a reverse proxy? nginx is one of the most battle tested code on earth and I don't see a benefit in replacing it with a r

Why would one want to replace nginx as a reverse proxy? nginx is one of the most battle tested code on earth and I don't see a benefit in replacing it with a ruby implementation. Also why are there a new http server coming out for ruby like every 3 years? Is it not suitable to just put nginx at front and the app server in the back?