Bengal don't have many Urdu speakers as such. Total Urdu speakers in Bengal is just 16lac out of it's 9.1cr population (2%) and 5.1cr Urdu speaking population of India and among that 16lac also, a large number of people belongs from neighbouring Kishanganj and Purnea district of Bihar.
Bengal definately has a significant amount of Muslim population but they are all Bengali muslims, not the urdu speaking ones. Same thing applies for Assam also. Infact the Bengali muslims of Bengal staged protest at various places against the govt's decision to teach Urdu in schools of Muslim dominated areas.
Infact...
more... Santali has more speakers in Bengal than Urdu but Urdu got importance in Bengal and recieved additional official status also just because of mere politics