Secret lies in the history. Earlier 12029/30 used to run IRY/20 rakes which were neither LHB nor ICF. That was a different set of rake which required weekly maintenance , and hence it ran 6 days a week with weekly maintenance on Thursday's. And on thursdays, ICF shatabdi rake was used for 12031/32 . Since now 12029/30 runs with LHB coaches, this practise of running it 6 days a week can be discontinued.