It also matters because of flight connections. A high frequency mainline flight + a low frequency regional leg = You can get a short/optimal connection time wi

It also matters because of flight connections. A high frequency mainline flight + a low frequency regional leg = You can get a short/optimal connection time with at least one of those mainline flight choices. But if both flights are low frequency, you wind up with a lot of connections hitting unappealing layover times that drive business to the competitor with a shorter layover.