Abrahams main reason for wanting to go to Washington in this episode was to get Eugene away from the threat, the termites. He stayed to help them and even though they killed all the termite why not wait a bit longer now the threat has gone and then have more people and therefore more protection to get to Washington and everyone could stick together? I can understand it from the writers point of view wanting to have another storyline for them etc but I can't understand it from the characters point of view.
because his main priority isnt just for ricks group, its for everyone still alive out there. the faster he gets eugene to washington the better. who knows how long it would of took for daryl and carol too come back, they might never had. abraham is looking at the bigger picture here so yeah thats why.