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Basically every person has a selfish nature, because that nature is a person's nature to fulfill his personal needs. Naturally, selfishness begins when humans are 2 years old because at that age humans have egocentric characters. Humans see everything from their perspective and have not been able to see from the eyes of others.

Some emotional causes for a person are:

1. Excessive attention (in childhood)

Excessive attention given by parents during childhood is one of the factors that trigger selfishness in someone. Attention Excessive makes parents spoil their children by fulfilling their desires. So that children are accustomed to getting anything without effort and struggle first.

Children are also not used to developing tolerance and patience with others. Usually this happens to the first child and the last child or single child.

2. Excessive protection (in childhood)

In showing love to children, parents often give excessive protection from various kinds of failures and mistakes. A feeling of deep concern also makes parents avoid children from jobs that can actually be done by their age.

3. Lack of Attention

In addition to excessive attention, lack of attention can also be a trigger for the growth of selfishness.

Actually, the main cause of one's selfishness is in the mistakes of parenting and environmental conditions. Because essentially all humans have individualistic traits, and social nature where if the person is more prominent individualism, his selfish attitude can be easily seen.

I think it is a mind set today. It is all about me and they don't care about anyone else. I have noticed this attitude at work and it is not about the company but how much they can take.

I think it is how they have been raised by their parents and you will find their parents were the same. Caring and loving for your fellow man has disappeared and it is a shame. Not everyone is like this and it is still out there but well hidden.

I have noticed lots of users on Steemit complain that they can't grow and that everyone is selfish looking after each other. This is not true and it is about getting to know people before they will help you. Maybe people have lost the art of interaction as they are missing out on a whole other side. 

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

For me, there are a lot of reasons why a person is having that behavior (selfishness) and his experience plays a big part on it. These my hypothesis on why people become selfish in today's world.

- Environment. 

They lived in a community(place) where the nature is being independent in yourself. That you don't need to beg and live in your own.

- Experience.

They had experienced mess and testing that made them realized they need to be individualistic - removing the idea of sharing in their minds.

- It is enough for them.

Sometimes we feel their selfishness but we do not understand that the things that they have is enough for them. Sometimes they feel they worked hard for it and deserves their reward.

That is a good question on why people are selfish. According, to me this is selfishness builds up due to jealousy and greed for more money I would say. If, you look at two person, say for example a person who is happy and is contemned will not at all be selfish and will be a kind of person who is willing to support. Whereas if other person who is jealousy with others success and is a greedy person you cannot expect good deeds from this person. Altogether it drills down to people upbringing and how their are behaving in the realistic world.