Why don't particles of a colloid settle?
Particles in colloid absorb either positive or negative ion preferentially from solution depending on there surface. This develops a potential on colloid surface called Zeta potential. Due to this potential colloid particles repel each other and can't coagulate.

Particle size also play a major role. With decreasing size surface to volume and hence surface to weigh ratio increases. So, same volume  of colloid  particles  have higher surface area than suspension. So, colloid surface have enough charge to keep them apart whereas suspension don't have.

Conclusion Both the point you've mentioned is responsible for prevention of colloid coagulation.