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It may be store policy but it unfortunately does not prevent it from happening. Two examples i can remember are "Gentle Alarm" and "Manhatten Project". Both I purchased and no longer available. Also not in my "not installed" list unfortunately.
I may have used the wrong terminology in my earlier reply. There is "unlisted" where the developer leaves the app in the store but removes it from the search. "Carcassonne" by Exocet comes to mind. It is still available for me to install but searching for it only shows the version by Asmodee.
Then there is the complete removal of the app. Gentle Alarm and Manhatten Project are 2 examples. :(
Then you should report the developers for breaching the Google Play Developer Policy.
I don't think they are around anymore.