Why don't they immigrate legally? That can be nearly impossible due to the backlog of applicants.

I just heard a tidbit on a radio interview that the waiting list to immigrate legally from India to USA is so large that it takes 30 years to get to the top of the list.

USA has different quotas for how many folks are allowed to immigrate from each country. Waiting lists are long. I would guess that its really long for countries where a lot of people apply for being on the list. India has a very large population, so a lot of potential applicants.

When you think about it, the size of our world's population is overwhelming. Quite a few folks try immigrating to Canada instead, which is somewhat easier.

Another problem is how repressive governments are in many parts of the world. Anti GLBT laws and so forth, as if a lifestyle not leading to procreation is criminal.

The world needs more lifestyles the don't lead to procreation; ironically for the sake of future generations. The best gift we can give to future generations is a livable planet.