I don't think that point to point is necessarily dead or even really correlated to all the airlines' declines. Rather, the entire category of US low cost carrier and ultra-low cost carrier is suffering, and that just happens to be all the point to point airlines. But this is happening even to the more hub-focused LCCs, like JetBlue (which is busy trying to upgrade into a traditional class-based carrier).
Now that every single legacy airline has a "basic economy", which is often competitive with the LCCs in pricing, there is no moat for the LCCs anymore. Legacy basic economy can be more attractive simply because of mileage programs and better frequencies (even if there is a connection); and legacy airlines have more wiggle room to lower prices in basic economy by raising prices in their premium classes.
It also does not help that the 737MAX fiasco hit some LCCs like Southwest particularly hard due to the practice of going all in on an aircraft type.
Now that every single legacy airline has a "basic economy", which is often competitive with the LCCs in pricing, there is no moat for the LCCs anymore. Legacy basic economy can be more attractive simply because of mileage programs and better frequencies (even if there is a connection); and legacy airlines have more wiggle room to lower prices in basic economy by raising prices in their premium classes.
It also does not help that the 737MAX fiasco hit some LCCs like Southwest particularly hard due to the practice of going all in on an aircraft type.