When the yachts are idle, which is the majority of the time, they are typically plugged into shore power and are thus just consuming electricity from the grid. The electrical systems of these things are typically far more efficient than your home because they must generate their own electricity when at sea.
As for the wasting of money, you'll note that most of the cost of building a yacht is labor because they are mostly one-off builds and can't take advantage of automation. The article mentions that they cost 10% of the purchase price per month in upkeep. The vast majority of those costs are labor.
These things are among the most efficient devices for transferring wealth from the rich to the middle class. I wouldn't discourage their use at all.