I have over 30 all positive reviews, and only few showing. The weird thing is, when I got few good reviews in the past, Yelp would call me and pester me about signing up for paid advertisement with them.
I refused or just ignored their calls.
Now, every time I get a positive review, next day it gets hidden. I don't get calls from Yelp anymore. The only reviews they stay are from people who are active on Yelp.

If a person who leaves you a review is not active on Yelp (maybe only has a couple of reviews and no 'yelp friends'), those reviews will be hidden.

Apparently, their 'algorithm' chooses which review is relevant and which is not. Or whether it's fake or not (if it is overly positive, it may be fake'...

It feels like pouring water in a bucket with holes, the reviews never seem to stay. I guess if you get hundreds of reviews it may start making a difference.