I see Format/Options/Typewriter Scrolling’s shortcut is Meta+Ctrl+T.
This is the only use of the Meta key I can find in Scrivener and it appears that Ctrl+Alt+T is available.
So why not change it and avoid having a fourth modifier?
The reason that Ctrl+Alt+T is not used is that the Ctrl+Alt combination is often used for accents and umlats in other languages. Using them in Scrivener often produces conflicts.
Hope that explains it.