HAproxy cannot serve static files directly. You need a webserver behind it for that.

Apache is slow.

Nginx is both a capable, fast reverse-proxy, and a capable, fast webserver. It can do everything HAproxy does, and what Apache does, and more.

I am not saying it is absolutely best for every use-case, but this flexibility is a large part of why I use it in my infra (nad have been using it for a decade).