Upside Down Earning Situations?
I think your starting premise (after all, the point is presumably to get people to use your product...not to use someone else's product, convert points, and then use yours for free) is no longer true. Airlines sell their FF points to third parties and these are now a major source of revenue for the airlines.
So the trend to cut points earned for flying and to encourage points earning via third parties simply reflects the airlines' desire to maximise revenues and profits.
The days of rewarding frequent flyers with free flights are gone. Loyalty is now rewarded through status benefits.