Why do backslashes prevent alias expansion?

Question

In the first part of my question I will provide some background info as a service to the community. The second part contains the actual question.

Part I

Answer 1

\ls only quotes the first character rather than the whole word. It's equivalent to writing 'l's.

You can verify it like this:

$ touch \?l
$ \??
bash: ?l: command not found

If \?? quoted the whole word it would say ?? not found rather than ?l not found.

I.e. it has the same effect as:

$ '?'?
bash: ?l: command not found

rather than:

$ '??'
bash: ??: command not found