Because those who work hard need something to entertain them otherwise they'd go crazy working all the time and never having any entertainment.
I know your question presupposes that the brick layer does not have time to indulge in such entertainment, but if no one bought the crap, the "entertainers" would not be making so much money.
Those "celebrities" make that much money because people are willing to pay money for their "service" or "product".
The children of the 80s who were brought up on greed and "material girl" ideals, are now raising kids who are even greedier and superficial than they were. These parents give their kids every stupid toy they want, and toys aren't cheap anymore. Ipods, cell phones, Computers, Internet, video games that both cost money and have their own monthly fee. Clothes and shoes and hair products and everything else so that they "fit in". Parents buy (or give their kids money to buy) movies and games and CD's that are rated for adults. Parents know their kids shouldn't be using this stuff, but they care more about their kids being "cool" and fitting in than they actually care about their kids well being.
You have white kids in the suburbs listening to rap music and trying to emulate gangsters, and the parents are ok with this.
It just gets worse with each generation. Each generation is more lenient with their kids than the last, and so it just keep perpetuating itself.
But you asked why, and it all boils down to insecurity.
People do not value themselves or their children enough to say "enough". Parents don't think enough of themselves to say I don't care what the neighbors are doing, I'm not going to let my daughter wear makeup and clothes that make her look like a street walker. Parents don't care enough about a kid to say I don't care if they get mad at me I'm simply not going to let them play a game with violence and sex and drugs and disrespect. Then those kids grow up disrespectful and wanting everything they see represented in their games and videos. ...And it just perpetuates.
People do not value themselves. People don't have morals.
They just want to have a good time and look good.
They don't care if their children grow up devoid of morals and integrity, as long as no one picks on them.
Sorry, the short answer is: We lack maturity and morals.