This is also a really annoying habit: giving a crap answer and then demanding an explanation of how it fails.

The meta-answer: if it was this easy people wouldn't keep asking about it. For decades now!

When I tried it fifteen years ago ssh insisted on reading the password from keyboard input, not stdin.

> Why not?

SSH reads the password from the terminal, otherwise it couldn't read the password on a piped input

ssh probably doesn't read the password from stdin.