Unfortunately the BDO which Walton, Adams, Hankey and OG Barneveld were part of is the equivalent of non-league football. The organisation (which I believe is now disbanded) was relentlessly stuck in the 1970's and failed to adapt to growth opportunities in the decades that preceded it. Tournaments were limited to one major a year and earning potential was non-existent unless you were top class. Most darts players had day jobs such as plumbers, builders and being postmen. The Lakeside was a iconic venue but one annual tournament was never going to help bolster the sport.
The PDC came in and offered players the chance of competing in several highly established tournaments each year, full time leagues and other competitions where prize money was significant. It allowed players like Mervyn King to go full time despite not being exceptional and he was making more than a in one week with them than what he would've got winning the World Title with the BDO. The PDC has also earned major sponsorship's and TV rights as well as forming global bodies. There's World Cup, European Championships and even Women's darts has florished massively plus regular Premier League darts and other smaller events.
There's also only been one televised 9 darter with the BDO whereas the quality the PDC offers is insane in comparison and this is what happens when you grow the sport and allow its competitors to do it for a living. I will never understand why the BDO kept darts in the stone age - a lack of foresight and ambition from the ageing and clueless board I bet but the PDC really delivered the game into a premium setting.