I don't doubt, that for a lot of people, they wouldn't visit the watermark without a way to have a little bit of seclusion. Not everybody wants to or is comfortable with just throwing a towel down and hanging out in their swimsuit. Plus, I'm sure with kids, it would make it really nice to have one of these.
Having said that, me personally, I would like the cabana, but I'm fine with riding the train over, throwing my sandals and shirt in the grass, and riding the slides.