Saying that particles explain why electrons all have the same charge presupposes that all particles are identical, but why should that be? Your particle theory has to explain why all particles of a given type have the same property; or rather, why there are types of particles.

The field idea, as discussed here, actually explains why all electrons are identical: because they're all quantized excitations of the same field. It's the quantization that really does the trick, but after all that's how we got started here.