Why was snsd such an anomaly fandom wise for a gg of their time?

They appealed to women too

I think they were (are)really versatile!

The members really fun !

An amazing vocal line!

Because everyone liked them. Men and women, old and young. Having such a diverse group of fans meant they would have a big fandom. Plus they had a ton of casual fans so it's not out of the realm of possibility to assume some if them bought albums too rather than only the hardcore fans.