Peter wrote in
:

I agree, but why can a PPL do this, then?

I am writing from the UK but I suspect it is the same in the USA.

In the US, by constitutional authority, everything is permitted unless
specifically prohibited by law, not the other way around. The FARs do not
prohibit flying at night over water, so it's allowed. Most regulations
are designed to prevent harm to innocent passengers, and private citizens
are assumed to be responsible for themselves; if they want to do something
dangerous to themselves, it's permitted.

In some instances, it's not that difficult, because there are lights, and
perhaps bright moonlight. But that can change quickly.

--
Regards,

Stan