Two years ago no one would have surpised if all 6 of these once-promising young players would be members of today's Top 10. It's like a divine conspiracy.
If you asked me in 2007, I'd have said I'd be shocked
of all six of those players were in the top ten.
Venus, Serena, Sharapova, Henin, Mauresmo had all won slams within the previous 18 months. We certainly didn't know Henin was going to retire, or Kim Clijsters or that Myskina wouldn't return.
And back then, we thought the 'Russian wave' was going to mean a lot of slam wins, not just a lot of players in the top twenty.
As for what happened to them, some combination of not enough talent, not enough skill, and not enough health. None of them never were as good as any of the current active multi-slam winners are right now. (I'm ot counting Davenport. I am counting Mauresmo.) But this is normal.
Promising young players usually DON'T win slams. Mostly they don't get to the top ten. And if they do, it's later in their careers.
Welcome back to reality, I guess.