I would say that the gap has increased between the big 3 teams (I would add New Zealand as well) and the rest. But that said, I haven't noticed any sharp reduction in the popularity of the sport in countries such as Pakistan, Bangladesh and Sri Lanka. Cricket remains as the most popular sport in South Asia. If you are looking for reasons why the quality of cricket has gone down in these countries, then it has been a topic that was much debated previously. There are a combination of different factors - financial troubles, corruption, lack of quality domestic leagues.etc.