Sailboats are more economical in terms of actually running them.
Relying on engine power is expensive, no doubt.
Motorhomes have similar initial costs & depreciation costs as boats, and, while they have higher maintenance costs than regular autos, they much cheaper than boats.
Same principles of being unbound, paid & free camping, operating costs (gas, propane, electrical), but the complexities of land vs water are orders of magnitude simpler.
While living on a boat takes some research, most people are already familiar with driving their own vehicles, with millions having experience with camping, trailers or actual RVs. It's really a bit of no-brainer - there are armies of motorhomeless by the beach.
They range of true bandit RVs to pretty nice rigs that are stopping by while on the way to someplace else.