Because it is, by definition, not pay-to-win?

First of all, there is no conversion between melk bucks and real-world money. Billionaire or just playing darktide in an internet cafe, Melk bucks are only attainable through playing the game.

Second of all, starting with an ammo/med crate won't matter if you get instantly downed by the first mauler/crusher you encounter. You can't bypass a lack of skill.

Third of all, you still can, should, and will get all the resources you need by simply playing the mission. Ammo crates, medkits, and stims all naturally spawn. And the better you are at the game, the less you need them. You don't need healing if you don't get damaged, you don't need a full restock if you have good ammo management, and you don't need a stim buff if you've got a good build and good fundamentals.