Why are recombination rates increasing in mammals?
If rates of meiotic recombination DIDN'T vary across species - THIS would require an explanation! After all, evolution creates diversity, not homogeneity.

I can only wonder that more recombination would allow for a faster diversification. The more DNA you shuffle, the more distinct each individual offspring may be (though I'm not 100% sure). The recombination rate has an energetic price, so not all animals recombine so much their DNA like later mammals. I.e. they needed a selective pressure to justify paying that price.

Perhaps it was useful for a group rapidly occupying the "vague niches" left by dinosaurs? This make sense, since the primary mammalian irradiation occured in the beginning of the Cenozoic era, right after the Cretaceous mass extinction that killed most big animals, including the biggest dinosaurs.

Unfortunately I have no references on the subject, it is just what makes sense to me, given evolutionary logic.