As these kinds of houses are very luxurious and highly exclusive, they have a much higher price bracket than the regular apartments that have a single story. The prices are also dependent on the location and trends in the market.
The penthouses being opulent and having upper-end security and maintenance attract a much higher cost of maintenance than regular households. The residents of the penthouses have to bear higher maintenance charges for society.
Although the views from the penthouse are beautiful, it comes at the cost of spending more time in elevators or using the stairs inside the house more often. This can become a difficulty in urgent scenarios sometimes.