A small correction: KakaoTalk is not an "all in one" app like WeChat. The main chat app does contain anciliary features such as gifting that enabled this exploit, but you can't call a taxi on KakaoTalk, you do that on Kakao T, a mobility app that also offers rental scooters, e-bikes, and train and flight booking. Similarly, even though the messenger app does have integration with its payment platform (cleverly named KakaoPay), the service itself lives in a dedicated app. It's like Google on Android where you could access bunch of services with one central ID, which I presume is why their apps have so many access points: they need it for themselves.