As you think about charging extra for things like a hot tub or sauna or heated pool, it's wise to be aware that those who don't have these things, generally have no clue how outrageously expensive they are to operate.
They go to their sport club, and the pool is heated, the jacuzzi and sauna is warm and running. But they don't realise it's paid for by hundreds of membership fees.
A single Airbnb (that isn't a hotel) has >one< paying guest at any time. So the price of having it all to themselves isn't shared. To cover those costs, they need to pay it all. But that won't enter the mind of most guests. A big extra charge that will cover those costs will seem absurd. Because they have no idea how expensive it is.
It's quite a challenge to explain this in a way that people will understand. Most won't.
We actually would like to provide these highly desirable amenities, but we're struggling to find the right way to price and position it. Raise the day rate and include it? Nobody in their right mind would include it unless per night rate can cover it.
...or an extra, substantial fee? Tricky. But it would give the guest the option.
Maybe pay per use? We can log the time and charge for it, I suppose.
Not sure yet...