There is a very strict interview process at google and they take hiring very seriously. They want to make sure that the candidate they hire would be a good asset and not just another employee. The resume selection procedure is also very precise.
The most common reason for you not getting an interview call can be as follows:-
Your application is not selected.
Your application is still in the pile.
Your CV isn't well build.
You don't have right credentials.
You don't meet the criteria.
Your luck didn't favour.