GitLab introduced their Pages relatively recently, maybe three years ago. The other two (Netlify and GitHub pages) are a few years older. I also vaguely remember something about it first being available in GitLab's enterprise edition, and later on being ported to the community version.

Not saying that there's anything wrong with it in particular, but it arrived a bit too late to set the standard for anything. People compared it to Netlify even when it was first announced.