As simple as possible to summarize the best way you can, first, please. Feel free to expand after, or just say whatever you want lol. Honest question.
That's because water is necessary to life.
When doing risk analysis something that is required to keep people alive gets a few extra points towards being accessible for, hopefully, obvious reasons.
If even something that is necessary for life is controlled due to the danger it poses, you can imagine why people would seek to restrict dangerous things that people can live without.