Perhaps the desire to emphasise those languages comes from the somewhat misguided notion that Urdu is more Islamic than Bangla; that Urdu is somehow closer to Arabic.
What Bangladeshi Islamic scholars should be focusing on, is not Urdu education, but on translation of relevant Islamic texts from Arabic, Persian, Urdu, and even English into Bangla.
Making works of Islamic scholarship accessible to readers of Bangla would go a much longer way than this futile move to push for Urdu.
Furthermore, it makes no sense to assume all madrasa students will go on to become Islamic scholars. The ones who do may opt to take up Urdu at a later stage in their education.
There is no way to defend the spending of tax-payer money on enriching Urdu in the way that has been proposed.