The TOWS is a simple ON/OFF system where no models are involved, just make sure that some conditions are satisfied. Is an ON/OFF logic, which could have been developed fool proof.
Nothing is fool proof. Somewhere along the line it requires human intervention or lack thereof and humans make mistakes. The more foolproof you think that you make it the more the human relies on complacency to just get by with the least amount of work.
I'll wait and see what the investigators analysis of the TOWs finds relative to its performance with average pilots, average mechanics and a combination of worst conditions in operation.