Or if they do, they ignore them. You get on the boat and just go. Evidently, easy access doesn't mean the same thing to everybody. Channel Islands National Park is among the least visited national parks and the likely reason is because the islands are separated by oceans. If you can't drive, most people don't go.
Some people get seasick.
Others come by plane. However you get there, the elbow room at Santa Cruz Island becomes even greater after Labor Day weekend. Now is an ideal time to kayak the islands. It's the best season. It's my favorite time.