Every person has a selfish attitude and wants more in life. Its a me-first world and always been.

However speaking from age one thing I notice as the decades and generations pass is that people are becoming MORE and MORE selfish. It's simply never enough

Currently we are in what I call the Entitled Generation

Young people today feel and actually believe they are entitled to certain things with no effort on their part. Just because they exist. This used to be called the Gimme generation but its actually gotten worse since then.

what causes it? I think its simple

Parents

Every parent has an innate desire to do better for their kids than was done to them. Provide more, make life easier and better. After all they are your kids and you want the best for them.

Unfortunately simply handing kids/people everything without having them work for it is not the best solution as we are finding out. Just because the new iPhone came out doesn't mean you NEED it, you WANT it yes, but you don't need it. If your existing phone, tablet, laptop, TV, car or whatever is only a few months, then live it until you learn the value of a dollar.

By giving the younger generation everything (or as much as we can) they ask for without teaching them that you have to work for things in life, we are creating new and more selfish generations each time. 

Couple that with basic human desire to want everything, more, better, etc and this is becoming a long term trend in society.

So to answer the question very simply

Why are people selfish in today's world?

Because that is how they are taught to be