I didn't say anything about who did or didn't use PEDS, I just stated that EPO was a contributing factor to some outrageous performances and drug tests have proven that over the last 15 years. EPO had a direct impact on the way the records and times changed overnight in the mid 90's. I'm not going to start naming countries and regions of the world wear drug-use is more prevelent, but I think people have a pretty good idea if you do your research.
About 20 years when you are a young 13:35-13:40 type guy then you think that maybe you can get down to 13:15-13:20 and compete internationally when the WR is about 13:00 or races are won in 13:10. But when everyone and their brother starts running 12:50, etc. then everything changes and less and less of those 13:35-13:40 type guys stay in the sport and develop (same can be said in the steeple and 10k, marathon, etc.) and that's what happened during that era. The gap exploded and the second tier guys disappeared.
Then people started hammering away at it around 2000 or so with a little post-college support here and there and now you have a lot of depth in the US at every event. Even the level it takes to be good in college is different. Sure, there were always international level guys competing in college, but now there are a lot more closer to that level. Just this year a sub 4:00 did not make the DI national field. Think about that for a moment.
In another chapter, but the same issue, look at some of the countries like Canada, NZ, Australia, etc. which have now set qualifying standards higher then the IAAF and IOC to compete at World Champs, Olympics, Commonwealth Games, etc. They have a few superstars, but no developing guys coming through because they can't see themselves realistically making that jump and it's discouraging. For example if you're a 22 year old guy running 8:35 in the steeple and the standard to compete in a championship is 8:25 then you have insentive to stay in it for 3-4 more years and go for. But if you're country is saying that doesn't matter, you need to run 8:15 and prove you will be top 12 or whatever then that guy will probably be done. He may be able to get to 8:15, but not straight from 8:35. And experience plays a big factor too.
All that to say that discouragement is a big reason people leave the sport, whether that's from lack of financial support, frustration with people who use PED's or just hassles and politics in their home federation. But usually if people see even a glimpse of light at the end of the tunnel then they will chase their dream for as long as they can.