Agama shastra does not stipulate that Perumal needs to be adorned with only one cloth. But for the comfort of Perumal tirumeni and that thirumanjanam is performed properly without too many clothes cluttering Perumal tirumeni, only a single cloth is adorned on Perumal. Only we have the restriction that we must not take a bath with a single cloth. The scriptural ordains apply only to us. Perumal is not subjected to scriptural rules! Hence, a single cloth is adorned for formality.