Because radio broadcasts have far shorter credit lists. Yeah to an extent you can do it with CDs but for 45s that is right out. However the license itself specifies "Reasonable to the medium or means" so this does not present a problem.
Surely you couldn't fit a read out version of [[France]] onto a 45? What matters is how much space (in what medium) the credits take in comparison to the content. Reading the credits to [[France]] may take quite a while compared to reading the article (maybe half as long? Possibly less, especially if you read the names pretty quickly), but media big enough to hold the whole article read out will probably be big enough to still have plenty of room to spare (reading the article might take, what, 30 mins? Can you think of a medium that can hold 30 mins of audio but not 45?). (These numbers are all guesses, I've never done any recording like this, so I don't know how long it's likely to end up being, but these figures should give a reasonable impression, I think.)
So "to clarify that attribution via reference to page histories is acceptable if there are more than five authors" is an attempt to fix a non problem using means of highly questionable legality under the terms of the license and non US law as well is deny wikipedia authors effective credit.
It also prevents us from bringing in CC-BY-SA from third party sources which makes it further unacceptable.
Yeah, that's about it.