User blog comment:WhiteArmor/The Masked/@comment-1932702-20100415093419

I agree with Prophz.. the Vizard have lived normal lives for approximately 100 years, i.e., no grinning Espada trying to hack your face to bits (Grimmjow), no maniacal indestructible Captain trying to rip you to shreds (Kenpachi) and no awesome super-cool Nihilistic emo guy trying to blast a hole in your chest (Ulquiorra).

Ichigo has repeatedly faced life-threatening situations where he has had to draw more power to defeat his opponents. The Vizard had no such problems, hence, no advancement.

It's kinda like evolution: it's triggered by a NEED for change. This could also be the reason why Ichigo is stronger than all the other Vizard (not sure if he is, though).