Why download rate drops day by day?

Hello everyone!

I have been reading this forum for a while but as you see this is my first post. So i have a question. I have relased my first app short time ago. I didn’t do any marketing or promotion. I got 250-300 installs daily for a week or so and then it dropped for no reason to 50-100 downloads per day.It has 6k downloads. I know downloads will not go up after somewhere and then starts to decrase. But i think this happened to my app so fastly. So i want your precious opinions, why this is happening?

Sorry for poor english.
(My app is a game.)

Check your app in appannie and try to find some clues there