“Hydrogen is the most common element in the universe and oxygen is the third most common element in the universe so who could be stupid enough to think that it is rare anywhere but here. “
The facts you mention while suggesting conditions for combining hydrogen and oxygen into water may exist with exo-planets in other solar systems, it is that combining of the two elements, and the conditions for it, which may NOT BE so abundant in the universe. If the mere existence of how much hydrogen and oxygen go to make up the known gases in the universe was the COMMON AND ESSENTIAL ingredient for estimating how often water “ought to be” present, then it would certainly be more present even in our own solar system than empirical science has determined so far.
Just take our own planet and what is described as key factors that make its ability to contain water - distance from our star and other factors, yet scientists still debate whether water was present in what went to make up the earth from the solar disk, or if it arrived early in the course of earth history from asteroids and other bodies that pelted the early earth. And none of the scientists on either side of that debate argue that water is here merely because of how “common” are hydrogen and oxygen.
Well scientists don’t know much. The theory of earth and other planets forming from a solar disk is still a theory and as such is not proven by any means. There are other possibilities. Also since most stars go through cycles of nucleogenesis which is how all elements other than hydrogen and helium are formed in the first place. So when a star ends its life most of the atoms will be oxygen, carbon and iron. Sheer proximity would allow water to form in massive quantities.