If it's not a duopoly, then why there's no competition between the play store and the app store to get developers or users from each other? The only tariff cha

If it's not a duopoly, then why there's no competition between the play store and the app store to get developers or users from each other? The only tariff change ever made on the appstore was as a reaction to an antitrust lawsuit and copied straight to Google. Just that is enough of a proof.