Let’s say I have a house on a river and no fence. So if people go into my yard to fish without permission they’re not trespassing? No, I paid extra for a house with that location, and the right to fish on it is mine.
Likewise, I’m paying for broadband, a WiFi router and the electricity to run it. It’s network trespass, although admittedly the nature of WiFi and the automatic connection mechanisms of operating systems means that people can accidentally trespass.
Can I fish there if you grant me permission to do so? Because it's impossible to connect to a wi-fi without the wi-fi either giving permission when asked or not giving permission and being denied by MAC filtering or password protection.