They may be trying to look their best (it's natural, I didn't wear my retainer to my wedding, my friend's gf had her braces removed for her graduatipn, so do many people...)
Ana Guevara does have braces and so does her sister... in case you get to see interviews... and I believe I saw another girl with upper braces, I think a swimmer, probably Australian. There's a fella with braces too but I don't remember anything about him.