Blame the stupid politicians of Jharkhand back then. Mamata Banerjee had agreed for transfering over the MGS division to ECR but wanted to keep DHN Division under ER, but Jharkhand adwitiyam politicians thought it is better to go under a so called 'Bihari' zone than a 'Bangali' zone!
Now these same dunderheads are busy doing 'Bahari' and 'Bhitri' politics...