easier to say "damage at xx,yy,zz, radius rr" than to say "render eleventy billion particles arrayed around point xx,yy,zz, velocity vv, vectors v1,v2,v3, ... v11tybillion, occluded by objects o1,o2,o3,etc,define each particle as a light source, etc etc etc"
the server doesn't give a rat's ass how many polygons or how big the textures are on each model, as long as every client has the same polygons and same textures.