Ultimately if you did this with Absolute Classic Rock you’d probably get a similar list; their playlist is very heavily stuck in those decades and the more modern takes on “classic rock” which PR plays don’t get a look in (Those Damn Crows, Florence Black, Massive Wagons, even Alter Bridge and the lamentable 5FDP).
I bet if you asked the Kerrang radio listeners to do theirs, that’s when you’d get a bit more variety. They seem to focus on 90s onwards, with a smattering of classic Sabbath, Maiden, Ozzy, Van Halen etc. It’s through Kerrang that I discovered I’d missed all 25 years of Billy Talent (bloody love that band now) and Rise Against (same) and learnt more about a lot of other bands I knew from one or two songs only.
It’s all incredibly subjective, and ultimately the PR raison d’etre is to play the older “classic” rock, hence that’s what the list will provide because that’s why the listeners tune in.