Hard to know why they died. But do know that Pennisetum 'Hameln' usually seeds about prolifically. And it's not a native.

I'm in Maine 6a and not all of my plants have emerged yet. The late emergers, like Joe Pye Weed have yet to peek forth. So, I'd give your grass another week or two.

It’s all dry and crumbling. I was wondering if I cut too far into the crown or something? It’s dead.

Mine did that same thing as yours above. I left them for a year hoping that they would come back. In the Spring last year I gave up and dug them up and threw them in the wheelbarrow. Well it rained and they were in there for about a week. Soaking it up.Next time I thought about them I checked and low and behold there were green stems coming up !! Yep I divided them and pulled off every bit of the dried parts and replanted in enriched soil. I'll get a picture later but they are growing !

Strange. I potted a few clumps to see what they do.