Gambling apps aren't banned on Google Play, but they're in one of the most heavily regulated categories. You need territorial licensing, approved country targeting, age verification, and explicit Google approval to distribute.
What Apple said
“Your app offers real-money gambling features but does not meet the requirements for gambling apps on Google Play. To distribute a gambling app, you must have a valid gambling license for the regions where you intend to distribute, implement proper age verification, and receive approval from Google Play before publishing.”
Google Play allows real-money gambling apps only in specific countries where gambling is legally regulated, only for developers who hold the required gambling license for those territories, and only after receiving explicit approval from Google. This is not a self-service process — you have to apply. Apps that appear to be gambling apps without this approval will be rejected.
While you're at it — Apple also requires these pages for every app.
Fix this rejection, then make sure you're covered on the compliance side too. Apple requires every app to link to a hosted Privacy Policy, Terms of Service, Support page, and Data Deletion page. No link means another rejection — just for a different reason.