The shore license was put in place to protect FL shore/wade anglers from the $20+ shore license the Feds wanted to impose on us a few years ago. At the time, FL was the only remaining state that did not impose a license for saltwater fishing from shore. As long as FL requires it's residents to possess a license while fishing from shore, the Feds can't do anything about it even if the license itself is free.
Also, the shore license allows FWC to know the number of Floridians fishing and helps with their estimate of how much money is contributed to the state of FL by recreational anglers. This is very important when the Feds decide who gets what fisheries allocations, Ex: commercial vs. recreational limits. If the Feds think they can get more taxes from commercial fishermen, that's who they give the bigger quota too. If they realize they can get more taxes from recreational fishermen, they'll give us a bigger quota.
Good luck,
Alex