Btw, I would love to see your CV/application letters since you are obviously doing something right with your applications.
No, but in all seriousness, I get (and appreciate) what you're saying. Considering my less than conventional educational background, I just wanted to exude my seriousness in the workplace. But as you mention, culture is extremely important at Google, and I trust that they have interviewed enough people to know who "fits" their organization; regardless of one's capacity to do the job.
Maybe.
Maybe not.
Selection processes which deal with a large number of applicants are often geared to find reasons for eliminating candidates.
In other words, if fit was the issue, the person who decided that you didn't, may not have any particularly good basis in experience for making that determination - could be they just don't like people in suits.
If you are the kind of person who wants to wear a suit everyday, then working at a bank is more likely to provide a better cultural fit - it's as simple as that. In other words, take each interview seriously enough to know when under-dressing is ok.