maybe the one who cursed Erden got jealous of his beauty so yeah, she/he curse him.

But wasn't his dad's statue also wearing a mask? (I'm not sure and I'm too lazy to check so, sorry if I'm wrong )

Yup
By the looks of it, its possible all the past Lords wore a mask too
So they've all been (since ancient times) "cursed with beauty" (maybe??) or like cursed to never be able to see that beauty??
Seems like in ancient times, the Halstead's either got cursed for some reason, maybe to do with demons, or maybe made a pact with someone/something that gave them protection but we're also cursed.