One of the (perhaps) unique factors concerning recreational boating on the east coast of the United States is the presence of the Intracoastal Waterway.
For people not familiar with the Intracoastal, it is an immense system of canals, rivers, bays, and inlets that runs parallel to the coastline of the entire southeastern United States. It is possible to literally navigate from Virginia to Texas without actually going out into the open ocean itself. The water that you sail on is salt (or at least pretty brackish) - but for the most part the navigator is preserved from the rollers and rough water of the open sea.
There are definitely hazards to navigation: In parts there is heavy commercial traffic: barges, etc. The waters are also tidal, and subject to shifting bottom conditions. But for the most part its a pretty forgiving maritime environment. In most cases you are sailing at most a few hundred yards from dry land - and more often than not, considerably less. There is minimal wave action along most of its length. In fact the wake from passing vessels is usually going to be the roughest water you encounter.
I guess I would argue that the demands in skill; judgement; and general seamanship required for piloting a small craft on the Intracoastal are vastly different from those required on the open sea. You could hand the keys to a reasonably responsible teenager and let them cruise a few miles up or down the Intracoastal with relative confidence; and after a relatively short period of instruction as to general principles of boat handling and piloting. If the engine fails, or the vessel runs out of fuel, they are at worst a few yards from shore or rescue. And - as alluded to earlier - virtually all of the Intracoastal is going to have mobile phone coverage.
The open sea? Even the warm, calm waters off Florida's east coast; are a vastly different proposition. If an engine quits; if the weather or sea state turns bad; if you get lost in a fog or at night; or if a crew member falls ill - you can very quickly find oneself in mortal peril.
I don't know that these two teenagers planned on heading out onto the Atlantic ocean proper. They may have planned a trip to a favored fishing ground in one of the many bays and estuaries along the Intracoastal. But somehow or another, their craft left the Intracoastal and entered the Atlantic Ocean proper, eventually drifting as it did several hundred miles to the northeast. An environment considerably more hazardous, and far more demanding in terms of skill and equipment.
