As I mentioned in my post, it is not about money. Spears has money. It's about attention. She and many other actresses who are sex symbols crave attention. As they get older they do "bolder" things to get that attention. Back in the day they would pose for Playboy or Penthouse. Not for the money but for the notoriety and attention. Sometimes, it jump-starts their faltering careers.
A few of these actresses posing when their careers were failing were: Kim Basinger, Shannen Doherty, Lindsey Lohan, Drew Barrymore, Farrah Fawcett, Cindy Crawford, Tia Carrere, Katarina Witt and about 60 others. It's interesting to note that with few exceptions this approach never works.
In recent years the actresses go straight to porn i.e. Ward and Olstead.