Marketing techniques have to change to keep up with the modern teen these days. If a corporation wants their ads to sell a product or service to teens than they have to keep up with what's "cool". Putting "cool" things like celebrities, major athletes and trends in ads help relate to teens. And relating to teens is key to selling to them.
At one time "MTV" ratings were about as high as can be. Then the modern teen's idea of what's cool changed. People lost interest and the ratings plummeted. "MTV" needed a new edge to get back on top. So they created a new show "Total Request live (TRL)". The way the show worked was that people would call in and request the songs they wanted to listen to and the video would get played. This ensured that what teens thought was cool was being played and subsequently ratings went up.
Companies like "MTV" use "cool" celebrities and athletes to sell to teens. If you turn on any channel you will probably see a celebrity endorsing something. This is another way to appeal to kids. "TRL" used "Limp Bizkit" to get back on top of the charts by featuring them on the annual "Spring Break Special". Other companies use high profile actors to sell products. Some examples: Beyonce for "Feria", various athletes for "Sprite" and Catherine Zeta-Jones for "Verizon".
"Sprite" has used many athletes in their commercials, but with an "anti-marketing" focus. Teens thought this was "cool" until they caught on that in fact it wasn't "anti-marketing". Sprite sales with teenagers went down quickly as more kids caught on. But then "Sprite" got a new idea - hip-hop music. They used urban culture to try to sell drinks and it worked. Hip-hop was "in" and they exploited it to make their product "cool" by association.
Teen's thoughts on what's "cool" or "in" at the time are constantly changing and ads need to keep up with what's cool to be affective. Teens are a huge demographic and corporations make a lot of money off them each and every year.