FWIW IMNHO "use the same thing for everything" is a technical reason ...
Nothing like logging in to a server running some old legacy app and realizing it's running some bespoke version of ancient Oracle Linux (or Gentoo or whatever you happen to be unfamiliar with, but some previous hire thought was the bomb) - and try to untangle what issues stem from the distro, and which belong to the application...
FWIW IMNHO "use the same thing for everything" is a technical reason ...
Nothing like logging in to a server running some old legacy app and realizing it's running some bespoke version of ancient Oracle Linux (or Gentoo or whatever you happen to be unfamiliar with, but some previous hire thought was the bomb) - and try to untangle what issues stem from the distro, and which belong to the application...