tl;dr: The tribes of long ago are now stretched thinly across kilometers of urban sprawl.

Body

Before the age of industrial revolution and exponential population growth, it was common for the majority of the human race to live in small communities where everyone knew everyone else. The amount of food available to us before industrialization was far lesser, as we could only use horse, cart, and hands to complete work, rather than machines. Since food availability correlates to population size, there weren't that many of us.

And it was always meant to be that way. Human beings are designed to function in groups of perhaps one thousand at the absolute most, 150 at best. The human brain has only a limited capacity for community and friendship; we can only properly connect with a certain amount of people.

We now live in cities that have a higher population size by themselves than the population of many countries combined in the Middle Ages. And so, we are totally unable to create friendships with every Joe and Jane we see amongst the skyscrapers in an average day, whereas we totally could have made friends with everyone in our little fishing village in 1469. We are designed to act in tribes, not legions; we are social, but not hive-minded.

We also live in an era of urban sprawl; the amount of real estate that an ordinary city would take up severely dwarfs the amount a city might take up in the Middle Ages and before. This is mainly due to our technological improvements to transport.

So we now have two things, mass passenger transport and human social overload; plus a third, secondary thing, which is portable print and web media as entertainment. Thus, humans, unable to know everyone, patter on their phones, oblivious to the world.

Solutions

Engage people in conversation on trains and buses. In fact, you should make a focus of your random interactions with people to be on public transport. If you like day game, do it as much as you can on public transport; it's a good way to break the monotony of the daily commute. People will appreciate you for making their lives that slight bit more interesting.