Volume material leads to bad shader complexity

I was making some material for fog. But I found the shader complexity is pretty bad if I set the material to volume and blend mode to additive. Even I just changed the color.
I found out that I can sorta optimise the shader by make the lifetime shorter, make the particle smaller or having smaller spawn rate. But it doesnt solve the root problem:(
Can anyone explain to me what is this happening? Thx! I will attach my material + particle setup.