It wasn't always the case -
https://en.wikipedia.org/wiki/HMS_Birkenhead_(1845)
The times they are a'changing though.
The river is the only clear area for an emergency landing in the city - ask Sully.
Maybe he was a student under a friend of mine who instructed in the air force. He told his students that in the event of a potentially unrecoverable emergency, he would say only one time......”Follow MEeeee....”