Lets bring economics into this!
In economics we learned of a little thing called the dominant strategy. It's when you make the best decision for yourself, regardless of whatever the other people do. And it's pretty simple.
If you lead a fast pace, you have less chances of winning.
If you follow the slow pace, you have a greater chance of winning.
Therefore in order to maximize your chances of winning...FOLLOW!!!
Since this applies to everybody, everybody will try to avoid leading a fast pace. So after the quick 100m start, the people up front are like "wait, dominant strategy!". They remember not to lead a fast pace, so they slow down or move back. But then since those guys moved back, you have new people up front who are like "damn, I'm up front. Wait, dominant strategy! Better slow it down to maximize chances of winning!". So they slow it down even further.
The result is the pace is slowed down almost to the point of a jog. Usually 60 pace in 1500m, 53+ in an 800m, etc..
This is freakin economics dude. It's one of those things where you can't blame any individual runner. After all, they're choosing their dominant strategy because they want to win. So they go slow. All it shows is that they're being smart and rational. In order for a fast-paced race all the time, someone in every single race would have to go against this dominant strategy, and be the sacrificial lamb. So whose it gonna be? The guy with the slowest pr? The guy with the fastest pr? The #6 qualifying time? There's just no way to ensure every single race is fast. And no way to enforce such a thing. And of course you can't punish any athletes for running a slow race, because they were just following their dominant strategy.
Fact is, slow, tactical races are just the nature of the sport. Appreciate it, embrace it. Enjoy it. And every once in a while when there is a boss front-running a 5000m (see 2003 WC men's 5000m final), because they're so rare it'll be all the more enjoyable.