In the end, there will be no single cause. Just another bureaucratic F-up. Here you have Feds pulling permits and the state calling it "fair" put against the locals wanting the lake kept high.
EGLE said failed Midland County dam in 'fair' condition after inspection in late 2018
The owner has said the state wouldn't grant required environmental permits to make repairs, because that department is essentially against putting a shovel in the ground if you might harm a worm. I can believe that, because the Macomb County Public Works Commissioner (who happens to be a Republican) cannot get approval from a Democrat-run State environmental agency for a project that keeps sewage out of Lake St. Clair because a man-made canal is now a "fish habit" (mostly invasive Asian carp).
About the only common theme is ineptitude from the state environmental department, which botched Flint and recently let the site of a Federal Clean up sit while they debated repair of a damaged roof. Guess what happened when it rained? I-696 green ooze. The years of inbred stupidity are starting to catch up.