Because it's their company (Harbour Lights) and they can! As Bob Irsay said commenting about his move from Baltimore to Indy "It's my candy store".

I happen to agree with Steve's theory of marketing skills learned from Bill's former association with David Winter cottages.

I think if you go to this site you will better understand why they picked the seahorse (hippocampus) to put on their lighthouses.
http://www.poost.nl/seahorse/index.html

Or could it have been that, Bill really likes seahorses!!!