There's an unfortunate cause of excessive app rating prompts — what's shown in search results/top charts/other areas is the average of the latest version, not the overall aggregate.

If you're at a company that does scheduled releases (e.g. once every three weeks), you'll need to continually ask people to review the app to keep that rating high.

Otherwise you only get ratings from new users and users that are discontent with the particular version. It's rare that people who have already rated the app 5-stars will continually go out of their way to rate the app 5-stars again without prompting.