Arrowhead has less than 100 employees. Helldivers 1 sold much, much less than 2. It has an all-time peak of 6,744 players, and that was seven years ago.
These were the conditions going in. I’m sure they’re trying to scale up and meet the insane demand for bug fixes and content, but that ain’t done in two months. In most respects this is a small developer who hasn’t planned for this kind of popularity.