p51guy, your "cause" is tautological.
The question is, Why?
An accident investigation is the means to determine the answer to this question in an attempt to prevent it from occuring again. That is now in process. A simplistic answer pointing to a single "cause" rarely, if ever, covers the mix of factors which result, (or not) in an accident.
We need to know what the crew was saying to one another so we can understand what the decision-making process, such as it may have been, was. We need to know if the TAWS provided any warnings and what, if any, was the response of the crew. We need to understand whether the airport was kept in view and if not why not. We need to know if they lost SA but didn't execute a missed approach or if they thought what they were doing was perfectly reasonable until just before the CFIT.
A number of plausible scenarios have been provided by thoughtful posters. Hopefully we will learn what happened once the information on the recorders is discussed publicly.
PJ2