I have been working on adding all street numbers for a small town of 40,000 people. Two years into this project, I am still little more than halfway done. Adding a handful of street numbers with StreetComplete might be "easy", but it is incredibly labor-intensive to add street numbers in an amount that makes OSM actually useful for navigation purposes. Google only managed to get their house numbers by forcing the world to do the work through ReCAPTCHA or by buying the rights to various preexisting databases.