Google Developer Console really should include a daily install/uninstall ratio graph - and seems like the obvious thing to have there (could it be that because it is very close to one of the factors which Google uses to rank an app, that Google deliberately not put that metric in the graphs ?).
I did however draw some graphs like that earlier and I noted something similar - i.e. the retention rate goes down.
Some factors that could be very neutral (i.e. nothing wrong with your app) - is that if the download rate (per day) is increasing, you maybe getting more people coming to your app (compared to the early days when fewer people visited or visited only because your description matched their search terms). As your app becomes more established it can start to appear in other apps’ Users also visited/downloaded section - this may raise the number of users being attracted to your app, but may no longer be the same “quality” (i.e. matched to what your app actually does). Or some such reason.
I think the existence of a competing app can make a difference also - esp. if you appear in that apps’ “Users also downloaded” list - in which case you may immediately do a fast comparison and rapidly dump the slightly lesser app. This may happen (slightly) even when the other app is worse - as some users will for some reason think that app is better (has better colors etc.).
Another thing to consider (and this is more significant probably) - is that with an “Active User” base of say 10K users, and 1K users coming in daily, your uninstall rate for that day will include the 1K users getting tired of your app, PLUS it will include the attrition from the 10K users “Active User” base (!)
This is one of the major reasons why nearly all apps experience stagnation - as EVENTUALLY no new install performance can outrun the attrition you are experiencing from your installed base (i.e. the “Active User” base).
Take an extreme example - if you are getting 1K app installs per day, and have 1M installed base - you can see how the behavior of your installed base will DOMINATE what happens.
For most apps (that are unchanged, or not radically get super-great) there will eventually be an “equilibrium” as the attrition from the installed base matches the daily retained installs (i.e. new installs minus new uninstalls).
If the app is good, it’s equilibrium point (for the “Active User” base) will be 5M, but if it is not so great the equilibrium maybe at 1M.
In fact, if your new installs minus new uninstalls daily figure is not big enough (or starting to dwindle following Christmas season) then your Active User base (installed base) may actually start to decline (since you are not able to replace the attrition from your installed base by the new net-installs that you get on daily basis).
Hope this helps.
P.S. - it is for this reason, the Active User base is essentially irrelevant (unless you have some way of galvanizing your installed base - perhaps by issuing notifications etc. so users revisit your app - the more installed base you have the more you can do this). Since many users install an app and fail to revisit it again much.
For ad revenue etc. - most of the time what is relevant is the “daily active user” or DAU.
If you are using push notifications, then the Active User base maybe important - as you can potentially make ad revenue from all the users who get push notifications (even if they haven’t used your app in a while).