Because they have a monopoly on old and especially niche knowledge/communities (also new niche knowledge/communities). As much as I hate it, that’s why I personally still have to use reddit sometimes.

Generally true, but still not true in a lot cases. Also the taste can often be really bad.

Heavily depends on where you live in Germany. It should be healthy (by law) and fairly tasty to drink everywhere in theorie, but in reality it is not. Especially depending on the landlord, old pipes can make drinking water range from tasting bad to being unhealthy. Yes, that is against the law, but landlords abusing the shit out of their position of power happens everywhere and a lot more than many probably realize.