The "looking at your fingers" challenge then becomes that you start to play "by eye" instead of "by ear" (or "by feel") which I find is very hard to overcome. Especially when you are improvising.
Though in a sense "by sheet" is just as bad.
Look at the audience, out of the window, into nothingness — or even close your eyes. As long as you're there.
Uh, why? Lots of pros use sheet music, especially for complex pieces. I’ve never heard of an orchestra conductor insisting everyone be off-book.
It’s one thing to memorize pop songs or whatever, but nobody is out there shaming people for not memorizing Rachmaninov
The orchestra setting has the extra requitement that the sheet is a tool for communication. "The figure in bar 83" is not a term you have gained an intuitive understanding for, but is needed to communicate in an orchestra setting. The soloist though often times plays by heart, at least during performances, so as not to get distracted / get tunnel vision.