Originally Posted by Andy

There are a lot of different aspects to the problem.
One is that the pay difference between WBFO and NBCA is not that large and WBFO is a great life.
You guys also missed one important aspect of why there are unfilled CA vacancies at United. Things are moving very quickly there. Monthly vacancies. The current open vacancy bid has 200 CA vacancies. 119 CA vacancies on the current snapshot are unfilled ... there are more than a few last minute bids which will fill most of those unfilled vacancies. Many will hold off on bidding up when they can do it next month or a few months later and time their training dates to something that works for them.

But the two biggest reasons why United, Delta, and American have so many upgrades available are due to 1) retirements and 2) rapid growth. Neither of which are present a Spirit and Frontier.
In fact, I have posted in the past that once the majors are done picking regionals clean, they'll be hiring as many pilots as possible from the ULCCs. And for the ULCCs, that means they will have similar problems as regionals for lifers - the seniority list doesn't grow, very few retirements, and lifers stay stagnant or even lose relative seniority at their airline because all of the FOs are leaving for legacies.
Maybe B6 will solve this problem for NK pilots, but B6 is also losing pilots to the legacies.
This is the reverse of the 15 or so years after 9/11.