There are a number of reasons that you might publish beyond Google Play. Most of the alternative Android app markets out there offer something to set themselves apart.
Free apps and promotions: Many app stores feature a free app of the day, a discounted premium app, or some other money-saving offer, making discovering new and useful apps simple.
App recommendations: Similarly, these stores might offer recommended apps that don’t pop up in the Google Play top ten charts.
Curated list: Some apps stores have a specific focus and a smaller selection of app choices that have been filtered for quality, age group, or purpose.
Localized portal: There are app stores that specifically cater to different countries, and may offer localized apps you wouldn’t find otherwise.
If you are an Android developer, you’ll also want to consider alternative Android app stores in order to maximize your exposure and ultimately your income.