They make money on the penalty default rate. They know what the average rate of default is, and they know how many people they plan to sign up. On average they make money. The 0% is to draw large numbers of customers in knowing that some percentage will default and of that percentage they will be able to collect on yet another percentage. This is why the default rate is like 24.99% or something silly like that.
It’s easier than you think! You can get your basic keelboat certification in about a month at a training place. Usually o Ku takes four weekends. Once you have that unused your belt, you’ll be able to rent at places and get some experience. The fundamentals of sailing don’t change, though with a bigger boat you will need to exercise some caution.
You can do it!