As a parent, I fly Southwest so that I can take advantage of the two free checked-in bags you get per ticket. Not having to wrestle several overfull bags of clothes on and off of the plane makes Southwest a great bargain for my piece of mind.
You should never have to pay for checked bags: just gate check the bags instead.
This new checked bag pricing has made the (already crowded) overhead compartments even more crowded. If your flight is full, or nearly so, there will not be enough overhead space for the carry-ons and the flight attendants and gate agents will start gate checking bags. Even if there is space, it may be toward the back of the plane, possibly behind one's seat.
This can be a big inconvenience for people who want to carry-on. If your carry-on is several rows behind you, you have to wait for the entire cabin to deplane before you can go back and get your bags. If you're on a tight layover, this can be seriously problematic.
As a result of this madness, the gate agents are always making announcements that they would like to gate check your bags (for free, of course).
Frontier: Checked baggage $25 web / $30 at airport. Carry on $30 web / $35 at airport. Gate check $50. Basically you're punished for gate checking, rather than committing in advance to either a carry on or checking before security. And it means no matter what you're paying for anything other than a personal item.
The Frontier gate check fee seems to only apply to items that are not eligible to be carry-on. It would not make sense to charge to gate check a carry-on item (as you are often required to do when the overhead bins are full).
That and the fact that they do family preboarding which really makes everyone happier (no screaming crazy kids in the lobby) and probably increases boarding throughput (no backup while moms wrestle carseats into window seats)
I'd guess they're comparing against airlines that charge for all checked bags starting from the first one, rather than airlines that give you one for free.
As in, if they had to pay to check bags, they would bring them all as carry on, where with southwest they can check them for free and not deal with. I'm not paying to check bags either.
