Because the certainty around the natural immunity is probably as questionable as the level of immunity from vaccination. Both are subject to epidemiological confirmation.
The potential harm of a re-infection or of infecting others is higher than the personal risk of being vaccinated.
I understand re-infection is something to think about. But infecting others is not an argument, as vaccinated persons can infect as much as unvacinnated ones. This is proven: https://www.youtube.com/watch?v=TKFWGvvlVLI
The potential harm of a re-infection or of infecting others is higher than the personal risk of being vaccinated.