It's hard to tell without photos, but it sounds like the crowns rotted. Long term wet weather and soil which does not drain adequately can do that. I lost a few well established grasses this year to rot, and my soil drains beautifully, but the wet weather took its toll.

I think donn's right. Worst situation is when it's wet weather with yo-yo temps. Recipe for rot. Been a tough winter/spring for the garden in most areas.

One good way to combat rot is to try to completely clean out the top of the crown when you cut the grass back. I am almost OCD about raking and even using tweezers to pick out any loose stuff like trapped leaves and such. Anything which can hold moisture can lead to crown rot.