Upvote:12
Because Delhi was deep within majority Hindu territory.
As @MarkC.Wallace pointed out, the partition of India was made along religious lines. Here is a map of pre-partition India by religious majority:
And here is a map of the final border:
While as argued the process was not entirely fair, one plainly sees that the partition plan did in fact broadly follow the religious border. Of the counterexamples you gave, both the Murshidabad and Malda districts are right on the border, while the Chittagong Hill Tracts was actually majority Bhuddist and therefore irrelevant.
Meanwhile, Delhi is 400km into Hindu-majority region.
Even if the partition commision was inclined to favour the Muslim state, there was simply no way to justify such an immense departure from the religious border.