There are a number of reasons why as alluded to in the article.
Firstly, the changing demographics of the black population in the UK.
Between 1980 and 1997 10 black players debuted for England and only 2 of them (Syd and Neil Williams) were born in England. Lewis, Benjamin, Malcolm, DeFreitas, Small, Slack, Cowans and Roland Butcher (no relation to Mark Butcher) were all born in the West Indies.
England has never had a track record of producing British-born black cricketers.
In 1997 Mark Butcher and Dean Headley debuted. I wouldnt include them in this discussion for 2 reasons. Firstly they are not a typical product of a system as they come from cricketing dynasties with both their fathers being Test cricketers (Headley, father and Grandfather for WI and Butcher, father for England) and they grew up around the County scene. Secondly, they are mixed race.
In the 10 years since 1997 only Alex Tudor has played Test cricket for England.
THere are a number of reasons why, as the article touch on some.
1) Less first generation West Indians brought up on cricket in the Islands.
2) The change in the education system where school sport in the state system was reduced since 1985 and beyond.
3) The explosion of the Premier League and the domination of soccer. Football is easier to get into, pays better, is more glamerous etc. No suprises that more people play it and want to play it. For example in my year group at school out of 130 boys only 2 played cricket and football was the only sport the school offered.
4) Small black population to start with so no real suprise that there are not that many playing. According to the CIA Factbook the UK (as the cricket team doesnt purely draw from England) the population is 2% black.
5) Fashion. West Indian/Black players were very fashionable in the 1980s and going into the 1990s due to the incredible WI team of the time. This led to a number being selected. In fact a Wisden from the 1980s suggests limiting the number of West Indians a team could have. We have seen similar with Australians being fashionable in the 1990s (Mullally, White, McCague, Gallian, Adam Hollioake, Ben Hollioake). All part of England consciencely or subconsciencely attempting to mimic what superior teams were doing at the time with inferior players.
The numbers may be down at the moment but I would suggest that the 1980s had an unrealistic participation level that was always unlikely to be maintained. The current levels are probably closer to the natural 'norms' even if they may be on the low side of that.