I think it has something to do with the transition from skeuomorphic metaphor to iconographic symbol.
As a skeuomorphism you might look at a magnifying glass symbol and say "that looks like a magnifying glass, which is a tool for making things bigger, therefore this thing makes things bigger".
As that symbol beds in and becomes part of language, it loses its connection, and its meaning is derived entirely from context and usage. I haven't used any Microsoft software for a while, but from my memory the floppy disc icon outlived floppy disks by quite a while.
You can argue that words shouldn't mean different things to what their etymology suggests, but that's the losing battle of a language prescriptivist, not a practical language user. I'm saddened when I see people use "utilize" instead of "use", or "everyday" instead of "every day" or whatever, but everyone knows what they mean. Like it or not, language changes.
So the magnifying glass has lost its etymology to popular usage. That's my theory anyway.