Baez's reason = publicity and fame. He thinks he is destined for bigger things than a small law office in Kissimee, Florida
The high-priced lawyers' reason = publicity and fame and, maybe, $$$$. They have to jump in on high-profile cases in order to keep their high-profile status. Also, Baez may have lured them with prospects of $$$$ after the successful $200K sale of Caylee's pix last Summer.
Casey's reason = snobbery. Casey didn't have an imaginary clerical job, she had imaginary managerial-type career complete with an office, company phone and flex time. Casey didn't hire an occasional imaginary babysitter, she had a high-priced "nanny" who took Caylee to expensive theme parks.
A public defender - not for Jose's "girl" !