Were they fools? I don't know but they did side with a bunch of losers. Mark also endorsed Fred Thompson in '07/'08 and he dropped out a week later. Fred had no energy and had no business running but Mark didn't see it.
Now they are all pretty much siding with Cruz and whether you like Cruz or not, he will be another loser. These radio hosts are good at a lot of things, but they are usually not so good when it comes to the Presidential primaries and telling us who should be the nominee.
I've been listening to Rush since summer of 1990. He has never endorsed anyone in the GOP primaries.
Instead, he waits until the nominee is selected and tries to polish the turd if needed (e.g. Dole, McCain, and Romney).
Notice what Limbaugh has said though during this campaign season.
1. He's acknowledged that he and Trump are at least friendly acquaintances but without endorsing Trump.
2. When asked, he's said Cruz is the most conservative candidate running but without endorsing Cruz.
3. When a viable candidate does or says something conservative, Rush praises him for it but without an endorsement.