It's pretty well-known that the people who stayed behind in present day India from UP, Bihar, other places were all lower class, illiterate, backward, poor people; who didn't have the resources to go to Pakistan. That is why UP, which was a prosperous state one time, has become renowned for its "Muslim slums & ghettos" today. In some few cases, some people opted to stay back in India because they had land/established family businesses. But by in large, if those people in India had the resources to migrate, they would have taken it. Same is the case, countless Sikhs fled from 1984 to avoid the massacre, & the ones that didn't have the resources to flee were slaughtered. Most religious groups (besides Indian Hindus) in India have had to face this massacre every decade on average.