A great number of U.S. based travelers simply won't consider flying on LY because as their flights don't earn miles into the flyer's non-LY frequent flyer plan.
Additionally, airlines don't typically plan flights based on where tourists live. Most tourists book in advance on low revenue fares thus aren't all that profitable for the airline.
Route placement depends, in large part, upon where the uberich traveler lives (e.g. the person willing to pay for C or F) and on the location of businesses which send employees on short-notice trips at full fare.