I have several friends who are in that tier of income living in SEA. Almost always these guys are either one, highly skilled IT guys (programmer, PPC marketing extrodinaire, stock trader, video editor, beat maker, copy writer, etc.) or two, own a successful online business (marketing agency, ecommerce biz, affiliate sites).
Lots of people who go to Thailand for the digital nomad dream end up failing because they fundamentally lack several combination of...focus, resourcefulness, discipline (both money and work), the intelligence, or are just plain under-prepared for the timeline it takes to get something going.