To me, the major feature of modern life that encourages the feeling of isolation is how big and how mobile our society is. When I was growing up on a very little island with only a relatively few people (sort of like a typical small town in the old days) everyone knew everyone. There was a feeling that you knew what your place was in society and you were secure in that place.
Nowadays, people tend to live in relatively big cities and they move around a lot. It is not uncommon to have no idea who your neighbors are. This certainly contributes (I think) to the feeling that you are isolated and adrift as a person.
Another factor that I think leads to this feeling of isolation is the fact that with modernization our family system has changed.
From what I have seen in India, in the relatively less modern regions people usually live in large families. Grandparents are not sent away to institutions for the old and there is no particular hurry for children to live in separate homes as soon as they are done with their education. A home with three generations living together is almost the norm.
But in the cities, where society is evolving fast towards the American model, the size of families is reducing too. It's just parents living with their children until they turn adults and then you have just a couple living in one house.
And as my colleague rightly pointed out, as things start to move too fast, it becomes difficult to adjust and find support and company. You are not sure that who you find around you today will be there tomorrow. A family is a group of people that you have known all your life and in that way you feel comfortable with. As families split up into smaller units, a feeling of isolation does set in.