Because the "environment" they were raised in allows them to be so.

Most people whom one would consider lazy are mostly the ones who have an "average to rich" lifestyle. These people are mostly teenagers who relies too much on their parents fortune. Since they know that even if they didn't do anything, mommy or daddys fortune and business would still be theirs in the future and will ensure their survival. They simply just don't have any motivation to survive or to improve themselves.