The Japanese soft-tip tour Asada plays on staged 29 tournaments this year:
- 12 in the lowest category, with winner's prize money of £3,500 (Asada entered 10, won 6)
- 13 in the middle category, with winner's prize money of £7,000 (Asada entered 12, won 7)
- 4 in the highest category, with winner's prize money of £10,500 (Asada entered 3, won 2 - the final event last week clashed with Ally Pally)
So that's roundabout £90,000 in prize money just for the 15 events he won, not even counting what he received in the others, or in non-tour events. Skipping these tourneys for major opportunities like the World Championship is one thing, skipping them for regular Pro Tour events would be quite a different matter.
Muramatsu was never quite this dominant on the rival Dartslive tour, but the basic idea is the same, hence he also played only sporadically when he had a tour card - trying their hand at the PDC is a big financial risk for these guys, even if they do get sponsorship for it (and I suspect many of their regular soft-tip sponsors don't care to pay them to do steel, so they'd have to find others for that).
Anyway, both these Japanese tours are only open to Japanese citizens and permanent residents, so all this only applies to Japanese players. Asian players from elsewhere don't have nearly this many opportunities to earn big tournament money.