Steve - a little perspective! That American team just ran 2.56 and the Bahamas became the third fastest nation of all time. If you genuinely believe the hype that there is just 300,000 Bahamians on the planet, you'll also believe that those Jamaicans who turn up to the Penn Relays or to Crystal Palace have travelled over to watch too
Note also - there's a great spread of countries involved and one reason is that in the past, small nations like Grenada and even Jamaica would lose their talent to America, as good kids were picked up to go to their college system, and then ended up running for them (some went earlier, for the promise of greater wealth e.g. Sanya). Now, athletes like Kirani James is training in America but running for his own country and getting financial aid, whilst Jamaica is in a position to hold onto its own talent and train them over there - the world has caught up!
Yes - we don't have the same number of sub-45 runners in one period as we had once, but the sport has changed, and until you recognise that, you will always be disappointed. I would LOVE us to be able to churn out a finalist for every major champs, but that is getting harder and harder. As with distance running, once you lose the chance of being at the top, participation falls down, as why work hard just to make a semi - so the talent pool shrinks
I also think you're being unfair on our junior talent - they don't have the absolute top end individual (apart from Clovis, perhaps) but there is a few more of them - and good competition that sustains itself from u17 into university level will help keep those kids (your Kirsty McAslens, Rachel Dickens etc) in the sport