Why are outdoor sockets only protected with 10A? Can it be changed?

It could actually be due to your light switches, which are being misused for the sockets. My outdoor socket is switched in the sub-distribution, where 16A is installed. Which makes sense according to the above calculation.

A circuit breaker with a B characteristic curve must trip at 5 times the nominal current, which is 80A. We're talking about 2.875 ohms of line resistance.

You can't generalize like that, it depends on the time. At 1.4 times the nominal current, it should trip after 30 minutes. At a factor of 5 within 5 seconds...

Yes. It is about short circuits or generally about circuit protection. It is not intended for personal protection; for that, an RCD (German FI) is installed in modern installations. This ensures that there is no current flow through the body exceeding 30mA. Although for people with weak hearts, that can already be enough to cause ventricular fibrillation.

It is important that with a circuit breaker with B-characteristic, in a solid short circuit, 80 A can flow. According to the standard, it must trip and disconnect the short circuit. If I achieve less than 80 A because the line resistances are too high, it trips via the thermal contact... that would be bad, especially since 230V is still present on the housing of the defective device.

But as already said... from 2 Ohms, the electrician must become suspicious...