Electrons are self replicating event configurations that are able to emit or absorb another kind of self replicating event configuration - the photon. The reason all the common particles are so common is that they fit into an ecology of particles. Each type of particle exists because it is stable within the context of the other particles it inhabits the universe with. Stability Stratagy Protons are probably a good example of a third stratagy, which is to be very stable dispite having many interactions. Protons generally do not decay, while photons are emmitted and absorbed all the time.
Protons appear to be more complex, allowing a wide range of types of interaction.
They survive by being resistant to events distrupting their 'event replication' mechanism. When the explotion of self replicating events configurations occured they would have been moving in all dimensions of phase space. However natural selection would eventally favour movement in a single direction in phase space. That dimension would be privledged, in the sense that while movement in the other dimensions may be optional, movement in at least dimension would be required for particles to work together in an ecology of interacting particles. This is the dimention we call time.