One of the reasons is that today the ONLY market with real money is the market of the Marathon. Losing sponsors and money, the meeting on the track have to limit the invitations to few athletes in top 20 in the World, and with no too much money. Another reason is that the distances on track (5000-10000-steeple) are TOO MUCH AFRICAN, and the interest of the organisers decreases, because is not possible to organise in every meeting an African Championships KEN-ETH (with some ERITREAN and UGANDAN) run by unknown athletes able to destroy the athletes from the rest of the World.
Look what happened in the steeple : with Shaheen at the top of his shape (2003-2006), the organisers asked every time an attempt against the WR. Of course, if you have to try to better the WR, you cannot accept that the second in the World (Paul Koech) can be in the race. So, in every race Shaheen arrived when all the other had still to go in the final furlong. At the same time, in all the competitions without Shaheen, the organisers looked at Paul Koech, that arrived 80m before the others. So, the event became only more PROMOTIONAL (the lower level of prizes), with personal appearance for the winner, before the race. This is one reason because at the moment the steeple is the weakest event of the middle distances.
So, what happens ? Young talented runners from Kenya and Ethiopia (look at the incredible improvement of the Ethiopian girls in Marathon)go now DIRECTLY to the Marathon, avoiding the mistakes of many top athletes of the past, that moved to the full marathon too late. This includes also athletes like Tergat or Gebre, that could run very much faster their Marathon if moving 5 years earlier to the event.
The multitude of young athletes running the event today means that they don't fear the distance, so the mentality changed. In Paris there were 20 athletes at 1:28:50 / 1:29 after 30km, only two years ago passage for ONE athlete and 3 pacers. The athletes know that, for winning a Marathon today, you must stay in the leading group, because it's not possible that, with 20 athletes together after 30 km, the winner comes from behind. Many are not able to finish, many finish in trouble under 2:07,somebody can attack the WR. At the moment, there are many athletes able to beat the WR in a race like Berlin, with perfect weather conditions : Gebre, Lel, Zersenay Tadesse, Kwambai, Kibet, Wanjiru, may be Robert Cheruiyot, and in short time other arrive under 2:04.
Also in training, there is something different.
About this, I invite to see the other thread, where I try to explain something new that we use with Kenyans.