I don't deny Barstool's popularity. But I think you are ignoring D&C's popularity, and the size of the demographic they dominate (which will not stick around for barstool sports guys).
I also think going from being a blogger to a radio personality is a leap...and not necessarily a seemless transition. Add into it the fact that they would be going from basically being their own bosses on the internet, where pretty much anything goes, to being on one of the largest radio networks in the country(not WEEI, Westwood one), where they are going to be expected to really toe the line.
They will not have the complete control that they want (or perhaps need) to be able to thrive.
Also, there is the simple question of how many of their readers listen to the radio. I would argue that you have a much safer radio audience with the 35 and up demographic that D&C dominate, than the younger demographic, who are moving further and further away from traditional forms of media every day.
However, if you bring them in on the midday show, let them build up an audience where they would have no real competition, then in a couple of years, they could be ready to take over for D&C when their contracts come up in a couple years. And by that time you wouldn't be taking as big a risk, because you will have some numbers to show they can handle drive time (and you have those numbers to sell to advertisers).