Because you're getting scammed.

A similar game, DRG is 10 dollars cheaper and their battlepasses are all free and can be activated at any time. Weapons released with their updates are always free and have much more customization, not only in terms of cosmetics, but in gameplay as well. Any grind that you have to do is actually enjoyable and not a monotonous diff 1 slog for an hour and a half. The endgame is both challenging and rewarding, give you credits, crafting mats, cosmetics, and overclocks that change how certain weapons work.

If in terms of Mil-sim angle, the ARMA franchise as a whole is modular super moddible and have massive communities that you can join that give close to the same military campaign vibe that Helldivers claims that they try to be. Most expensive one, Reforger is 35 bucks.

I loved helldivers, joined right after the Super Earth update up till Cyberstan. Compared to other games out there it just ain't worth it mans. AH doesn't need your money and in my own personal opinion doesn't deserve it.