In the end, you're most likely going to get rejected for a bunch of common reasons:

1 - Someone else appeared to be clearly better than you (see 2,3,4,5)

2 - You didn't have good enough communications skills

3 - You didn't have enough 'perceived experience' or the right set of skills

4 - You don't appear to be a good fit, personality-wise

5 - You priced yourself over what they thought you were worth

#2 and #3 are what most candidates need to work on. Communicating that whatever skills they have are more than satisfactory, preventing #1. On the other hand, if your personality rubs the interviewer the wrong way (#4), there's usually possibility to recover.

In the end, most people don't need explicit feedback. They just need to pay attention to the verbal and non-verbal cues given off by the interviewer. Unless the interviewer is negotiating compensation, there's usually no need for him/her to have a poker face. 9 times out of 10, you'll get clues as to what the interviewer isn't liking about you.