Because she busted her *** all day long picking them up hahah sorry could not resist...:)
Because you can buy in 5 minutes what would take you possibly years to find. You see, she is an importer of fine exotic specimens from the Maldives and Seychelles.
The same reason people pay more for precut carrots- because someone else did the work.
If people will buy a pet rock, they'll buy a sea shell at the sea shore.
It's the old shell game in one of it's early forms