But letting search be affected by tags more than the description text would be a way to let the devs prioritize the most important keywords. Other people don't really need to know anything about them.
As opposed to putting "tags" in the app title (motivation for all calendar apps to be named something with Calendar) or X number of times in the description text (motivation for unnatural copy).
Disclaimer: Based on what little I know about search priority in Google Play.
Steam implemented tags (and, appropriately enough, a personalized 'discover' queue) and it helps.
On Amazon's non-app store, you can also buy search ads. Apple could implement something similar and take a larger cut of the paid install market. There are search ads on Google Play (see: http://adwords.blogspot.com/2015/07/launching-search-ads-on-...).
