The issue is really that Kakao is not just a comic app.

They are basically the Meta/Facebook of South Korea, one of the most valuable companies in the whole country, and they are in quite literally every facet of South Korean life.

They do instant messaging (KakaoTalk), payments (KakaoPay), banking (KakaoBank), public transportation (Kakao T), games (Kakao Games) and probably way more I'm forgetting. If you're in south Korea you cannot live without Kakao almost.

Webtoons are not a significant portion of their income, but they have so much disposable income and such a drive to go after pirates that they don't care.

Their actual audience in South Korea is very anti piracy too and support these moves. It's a very similar case in Japan, but not even the richest Japanese manga publishers are as filthy rich like Kakao, they mostly spend their resources fighting piracy within their borders and leave it at that.

Also the monetization model you're describing is unfortunately the most profitable currently. They employ it because it works. Webtoons are also by far, and I mean by faaaar, the most consumed comic format. Majority of the public is now reading comics on their phones and Webtoons thrive there. So there's a very big financial incentive to go after mobile apps because of it.

Apparently age verification is an issue and needs korean phone numbers too

They apparently made a lady have a miscarriage and dont pay well