So, why is this game at skirmish scale?

This isn't a complaint or a critique, I love skirmish games and I think the base game and campaign rules are really cool.

My question more stems from the setting of the game, it's trench warfare during an alternate WWI. Mass graves and casualties, weapons that destroy entire cities, the works. I feel like the battles would be a LOT bigger than, like, 10-20 dudes shooting each other at a time.

Why do we command such small forces in this grand, intercontinental conflict? What's actually taking place during a battle? Is it implied that the games that we have are taking place in a more grand event happening outside the table space like 40k? Are we commanding warbands that just aren't part of the main conflict, taking missions in no-man's-land away from the front lines? Am I thinking to hard about this?

Again this is NOT a critique of the game, not at all. I think the game works VERY well and the vision is really cool. I guess I'm just looking for more context to what WE'RE doing in this world when we play.

Edit: I can't really get to you all, but y'all's answers have been super helpful. Didn't know Mordheim designers were a part of this game which gets me super excited to play.

My question was a lot less about model count and a lot more about the implied scale if that makes sense. Like, battle tech has a MASSIVE scale of battle with fewer models, even without the GIANT mechs.

The idea of our warbands sneaking around no-man's-land doing specialist missions, scavenging for relics, and doing recon missions while the overall conflict is in a lull is really neat. I'm super excited to get into this :D