It has a few old things unique to it in our support matrix. It's the only distro with openssl 1.0 so a bunch of API and related things are different. It's also the only distro where systemd socket activation doesn't work if your service has more than one socket, because its version of systemd predates the LISTEN_FDNAMES env var.

Also, it is old enough that it's going out of LTS soon.

CentOS 7 may have been released in 2014, but the software it shipped was already quite old then.

As a datapoint, CentOS Stream 9 [0], which was released in 2021, and which RHEL 9 (released in May 2022) is based on, is already ~60% out of date according to repology: https://repology.org/repository/centos_stream_9.

Also: In computer time, 8 years is "very old". That's longer than the "mainstream support" window for Windows 7 was (from 2009 to 2015), and about as long as the mainstream support window for Windows XP (from 2001 to 2009).

[0]: CentOS "Stream" has a different release model and appears to be a bit of a rolling release as I understand it? But that would cause it to be more up-to-date, not less.