There are many situations where the player might want to have a tighter formation, either for easier manoeuvring or to exploit a terrain feature or something. I've found that long range splash damage weapons disregard all that and make the only viable option to spread everyone out as thin as possible, and either camp or rush instead of manoeuvring.
If I could get 10,000 dudes on screen at once, damn right I'd spend the time and add artillery, fixed and moveable and naval and airborne and all sorts. But with tiny little bands of men it's a bit ridiculous to have such powerful weapons around. It would be like call of duty 8v8 with a tank on each team. Or chess with a machine gun. Or pokemon with nukes.