Hi chin.billy.leung, in my opinion, when you speak "왜이렇게" real fast, it sounds like "왤케". So we often pronounce "왤케" regardless of our intention. And yeah, since most old people speak slowly, you can mostly hear it from young people.

For now, it is mostly chatroom or sns language. BTW, there is a beverage called 왤케셔(WELCHESHER) (it is composed of 왤케+셔(sour)) http://www.dalkomm.com/portfolio-posts/%EC%9B%B0%EC%BC%80%EC%85%94-%EB%A0%88%EB%93%9C/