La Guardia, like Washington National (DCA) labors under "perimeter rules" that limit outbound flight distances. These are holdovers from when Idlewild and Dulles were emerging as the long-distance airports for NYC and DC, and are mainly politically-enforced.

Long-appearing segments like LGA-SNA usually, upon closer examination, entail a stop in DFW or some such; the flight number doesn't change despite there being two sectors to the segment.

LGA is a critical O/D market as it's usually easier and quicker to get into Manhattan compared to JFK; in the case of DCA the airport's close enough to the District that it presents noise pollution issues around the Capitol and White House.

But I have only two words regarding xONEx-unfriendly hubbing policies. Gat. Wick.