It is all about marketing
It is all about marketing. Sure, there may already be "enough" service from other carriers, but I would guess Frontier is taking the side "we offer more on our system, so fly with us...." I feel travelers get accustom to an on board "perk" or type of equipment and hence influence a carrier adding a certain route or location.
I would also guess that this is but one part of a larger North/South expansion. What is next LAX-SFO-???? OR SFO-LAX-??????
Frontier, like SWA or JB, think things thru with the markets they serve. I think there is a bigger picture coming soon.
Yes?