They indeed are shipping with really good libraries these days but no matter how good they are, there is some level of doubt that they fail to alleviate and they get deployed behind nginx or apache httpd anyway.
It seems more like they are deployed behind load balancers, because load balancing is a specific job that it makes sense to do with a separate piece of software. Admittedly, that separate piece of software is often nginx, but there are other popular options, and I don't think very many people use Apache that way (though I could be wrong).
