If WEBTOON offered to pay me between $1000 to $2000 a week to make my comic, promote it heavily, help me develop a massive audience through that promotion, and the only trade-off is that I couldn't post it anywhere else online for the duration of that time, I'd be insane to turn that down! Especially since they don't retain IP rights to any of what I make, and their distribution rights end as soon as the contract does.
It's actually a stunningly good publishing deal for an independent comic creator, or any author for that matter.
It's understandable to prefer one website over another, but to think a creator is somehow 'betraying' their readers by choosing to publish on one free-to-read website rather than two, when they've been offered such a good deal to do so, is rather silly.
If you really like a comic, and it's picked up by WEBTOON, just go read it on WEBTOON. Their app and website may not be as good as Tapas, but it's serviceable. There are loads of great stories there you're missing out on.