Rating counts are the best public proxy for how long an app has been accumulating users. An incumbent with 400,000 ratings has years of momentum behind it; one with 300 does not.
That is the entire claim. A high rating count is not quality, not revenue, and not a download figure — plenty of enormous apps are mediocre and plenty of small ones are excellent.
We show the count and never the average score. An average across a handful of ratings is noise, and presenting one as a judgement of somebody's app would be inventing a verdict we have no basis for.