Most ninjas we have at the moment weren't around during the no level cap thing.
Main problem that makes people give up on ninjaing is that to survive you have to stay with the group. Flanking gets you too easily killed nowadays. And the biggest ninja nerf to date was not level cap. It was pocket bamboo removal
In either case. Not everyone is cut out to be a ninja, so they either quit the game or leave the clan. Another problem ninjas face is that the playstyle is really restrictive, so people get bored.
We're still around. Just not as active. I currently play primarily on siege just to do some simple admin duties, otherwise I play other games.
Auphilia, I think he's talking about the January 2011 patch that increased experience required for levels. I used to be level 38 or something back in the day with 230 wpf and a 106 speed katana ;)