I can think of a few reasons.

1) If I buy the jersey the (real)team gets a portion of
the sale. If it supports them financially good.

B) Because I have some connection with the team. Case in point, I
work for CSC (ok, no smartassed remarks about that) who as
a corporation sponsors a pro team, I have a CSC jersey that I do
wear as both some allegiance to work, and the team.

thirdly) I am a sponsor of a team. No, really. The members of
the Serotta Owners forum all kicked in enough money to
become a sponsor of the Sierra Nevada team.

5) I have a Serotta Jersey, I ride a Serotta bike. Not the same as
a pro team, but it is a rolling billboard.

thats about all I can think of for now.

Marty (confirmed glue sniffer and tubular user)