Madaras eyes we also got to see all the time, unlike sasukes which we never get to see plus dragon master already showed a scan of Sasuke casually sipping a drink with it activated. Kishi obviously has it covered up unless sasuke needs to activate it to sip tea, which I highly doubtDont know if his rinnegan is still active in his left eye or not so cant claim he cant deactivate it, besides madara has a similar hair style covering his left eye.