There are many reasons that the war has been at a standstill. Foreign support of the military factions has resulted in a standoff. There is tremendous commitment of Pakistani volunteers that provides openended recruits and helps the Taliban replenish their supplies. Masoud also received technical support from non-government sources. There is also support from Iran, Russia, Tajikistan and Pakistan for Masoud's forces.
People join one side or the other in order to survive.
They might join because of ethnic affinity. In fact the Pashtuns are in an ethnic standoff. Military actions cause more military actions, but there are no visible alternatives. The Taliban have pledged to disarm the population but they are not up to the challenge. If the Taliban obtain control there still would be rifts between the nationalists and the internationalists, the west against the east, the traditionalists vs. the modernists.