I thought it was the horrible compression and oil burning. Apex seals seem to last if you don’t do silly things to them but you can’t solve inherent issues with the cycle design.
For comparison, rotaries get about 100psi of compression, a modern gas car can more than double that. More compression, more efficient burn.
I've read that oil burning (which is directly tied to the apex seals) has been fixed in modern engines. Compression is a somewhat configurable matter, and can be high in a low-torque generator (battery hybrid) application.
For comparison, rotaries get about 100psi of compression, a modern gas car can more than double that. More compression, more efficient burn.