no, it's because they want a foot in the door of ppa market. it's logical, that they offer ppa ads in order to eliminate affiliate programs by widening their portfolio. it's a strategical decision, but a) they'd be dumb to kill their cash cow cpc and b) as publishers will probably earn less through cpa in combination with higher risk they will discard it. so cpa is doomed to be an add-on.
you don't like cpm, we don't like cpa, so let's meet in the middle and don't let greedy advertisers disturb the market balance.
It has nothing to do with what I like or don't like; it is what the marketplace has to say about the situation. FWIW, I don't think CPC is going away; I do think there will be a sizable number of advertisers who switch to CPA because it will give them better control over their ad spend. Choice is good.