Why do not you ask your fellow citizens who try to come to India with illegal visa??? Guys i am not sure, if PDF posters really beleive that this illegal immigration do not exists..
This summer, i went to Bhubaneswar. Even in Bhubaneswar, most of the daily worker and technician people are illegal bangladeshi people who are doing work...Again, BD people are easily assimilated in eastern part of India due to simillarity in food habbit, body structure and above all, they look like Bengali, Odiya or Assamese people...I am not sure about the extent of illegal immigartion to INDIA, but at least in Bhubaneswar, i can find good number of people are residing and working...And above all, it is very easy in India to bribe some official and get the ration card and stay long time...And on top of it, in my community, people invite to few of the cooks on marriage function, they are very good in our area from BD community in Bhubaneswar.
Again, coming to your question, even i do not have any answer, why people from BD are immigrating to India when your GDP is much more than India...