Red Hat was the first really organized non-hacker kind of distro. Mandrake (now Mandriva), Suse and many others forked Red Hat a long time ago. After Red Hat Linux 9, they decided to stop putting out these desktop releases and instead focus on Red Hat Enterprise Linux. This is where Fedora was born, to follow up on their "for the people" product. With this move Red Hat lost a lot of desktop users who switched to other distros. Meanwhile, Red Hat has the most corporate appeal, it's the #1 distro on servers.
And in many ways it's still the standard for linux, so if you tell people you know linux, they halfway expect you to know "the Red Hat way".