>>1614948In a forest, they're taking their nutrients from live trees, dead wood (logs), dead leaves, mulch, etc. and less so from the soil itself.
Again there are exceptions, but soil/grass mushrooms are generally not edible, not choice, and tend to be (to varying extents) toxic to humans. Maybe because they're out in the "open" grassland and obvious to possible nibblers they've developed more toxicity as defence. I dunno. Just how it is.