iTerm2 where is [ ] keybindings? Is there a reason why ALT+8 / ALT+9 does not produce [ and ] in iTerm2 ?

I'm running with defaults and a .bashrc/.bash_profile that produces the correct result in Terminal.app.
iTerm2's defaults for the Option keys are called “Esc+”, which basically means it will type an escape character (\033) before any character you type while holding down Option. To get the same behavior you see in Terminal, go to Preferences > Profiles > (your profile) > Keys and select Meta under both "right option key" and "left option key".