Why isn't this available for purchase?

Why isn’t there anything to buy?

Even if you would probably now like to read that the mineral oil industry has “sustained” the supposedly ingenious inventors for obvious reasons, it is quite different. @Tellensohn has already formulated it nicely. If a motor would run simply with pure water, without further energy supply, then it would be a “perpetuum mobile”. Energy can only be generated when reactive substances are brought together. And so that water becomes reactive, it must be converted into hydrogen. This then reacts with oxygen in a so-called “nall gas explosion”. However, water cannot simply be converted into hydrogen, for this purpose energy must be supplied. It is smarter (and probably also more efficient) to invest directly in the drive of the vehicle instead of going a way around – except, you would like to catch up with lay people. I can quite imagine that the above message in certain groups of persons (usually susceptible to conspiracy theories without significant physical knowledge) is likely to be of the highest interest.

I’ve never claimed anything, just asking why there’s no hydrogen-powered scooter to buy.

Because hydrogen is very difficult to store (see BMW Hydrogen 7, where after a few weeks the tank is empty), and because it is probably more expensive than gasoline.

Then you should think about when it is time to quit the job at the mineral oil industry.

I work in a pizzeria. :))

Fact is: Without energy supply, no object moves on the earth, because the resistors are constantly working against it. This is zig-fold, you don’t have to discuss it. By the way, the TÜV only checks traffic safety, not the plausibility of the product data. The link you added is also clearly described, which makes the vehicle drive: with hydrogen, not with water. This is a relevant difference, because hydrogen reacts very strongly with oxygen. What does water do if it comes into contact with oxygen?