Burnout from doing same thing over and over.
There is a ton of CRUD and mind-numbing tasks you have to churn through to get to the interesting parts, and I have been doing the boring parts for 20 years. The goals barely changed, but how we implement things has. New ways to build, new way to deploy, new languages, new frameworks. Just keeping up with it is a struggle.
I think my next project, I am just going to go Rails. It's my way of giving up :)