Getting your app published on Google Play is fairly easy. You basically just upload an APK and with how little Google reviews apps, you can get almost anything published. F-Droid on the other hand has very strict standards (which is a good thing). Since I published an app myself on F-Droid, I can tell you that fulfilling those standards does take a lot of effort, and thus a lot of love from the developer.
This creates a filter: If you care enough about your project to go the extra mile to fulfil the F-Droid requirements, you probably also care about making a good product. If you don't, you also won't be motivated enough to publish on F-Droid. There are countless open-source projects which sort-of work but are left behind, usually because it was someone's side-project. This is ok as well, because it's free time that most people are spending on Open-Source projects, but as a result, most open-source projects are actually not very mature. They just never make it onto F-Droid and don't go viral.
Getting your app published on Google Play is fairly easy. You basically just upload an APK and with how little Google reviews apps, you can get almost anything published. F-Droid on the other hand has very strict standards (which is a good thing). Since I published an app myself on F-Droid, I can tell you that fulfilling those standards does take a lot of effort, and thus a lot of love from the developer.
This creates a filter: If you care enough about your project to go the extra mile to fulfil the F-Droid requirements, you probably also care about making a good product. If you don't, you also won't be motivated enough to publish on F-Droid. There are countless open-source projects which sort-of work but are left behind, usually because it was someone's side-project. This is ok as well, because it's free time that most people are spending on Open-Source projects, but as a result, most open-source projects are actually not very mature. They just never make it onto F-Droid and don't go viral.