Trench Warfare with melee focus

I am thinking about world where global conflict simmilar to WW1 lasts way longer and depletes nations resources which causes more focus on close quarter medieval like combat. Despite technology being simmilar to that of WW1 soldiers armed with shields and swords - having only a few cheap one shot rifiles per squad. And only most elite troops having bolt action rifles and smg etc. Masses of trench warriors with elite armed like actual proper WW1 soldiers.

I am wondering if gunpowder is even that expensive in order for this to make sense. But maybe reason for this would be that bullets and rifles need more sophisticated tools to produce?

I am open to suggestions and opinions on idea like that, there is also kind of magic there but it's not important for this topic