Because you can pay once for a set of batteries and fly it year after year.
That's not my experiance, a plane of that size will require much more than $50 in batteries. Although reviever batteries ast 5 years or more, the heavy load on electric motor batteries last about a year. Unless you don't fly that much or are satisfied with much shorter flights, and don't mind waiting for them to charge.
I don't think those flying pattern back then would have wanted them to be that quite, just less noisey.