AltGr+8 is reasonable enough that I don't feel like learning a new layout.
Ctrl+AltGr+8 is involved enough that I might as well press Esc.
A lot of software developers are unaware of the AltGr[1] key or even assume US ANSI layout altogether so as a user I have been trained not to take keybindings involving that layer for granted.
As a real world example of similar issues, there's piece of software (I think it was telnet or mosh, but I apologize if I misremember) where Ctrl+^ is used as an escape sequence. This doesn't work for me, possibly because caret is a dead key[2] on my keyboard. For some reason, perhaps related to using scancodes instead of key codes, Ctrl+6 happens to work in that application.
