Because it is a bad idea to open a network by default? Together with the WiFi you open ftp and telnet. So you have full control over the machine, when you are able to use a search engine. I don't miss the times when scott tiger opened 80% of the oracle DBs. Beside the security issue most people doesn't want that theire microcontrollers use by default as much power as possible. They want to have a easy way to turn the features on and not to read a lot of manuals and community articles how to switch unwanted features off.