Probably because playing 30,000 hands each for a chance to win a share of $200k is spectacularly not worth it for those guys.

And Durrr is known for not finishing his challenges...

Because both play massive cash games where you can make/lose $200K in a night, and not have to play 30k hands...

Dwan is something of a reclusive/shady figure these days. Also it's unlikely he's currently playing anywhere close to his skill peak/ the skill level of the four selected - once a poker pro has achieved a level of fame commensurate to his, they can live comfortably for the rest of their days bleeding wealthy amateurs who get their kicks from playing (and losing) high stakes cash games against pros.

Don't know about Blom - probably just insufficient action for him (couldn't tell from the article, but it seems likely they're playing play money cash games, with fixed prizes for players who end ahead).

They gave Isildur a ring but he didn't handle it very well.