I think Evernote's reason is actually surprising reasonable. I can imagine there's really some UIs that unreliably mess up leading and trailing spaces, and if they want to support those platforms, that means no leading and trailing spaces in the passwords. No spaces in the middle is too bad, you can disagree with their decision that "1.5 percent more entropy isn't worth the effort", but at least it's a reason, which is more than you can say about systems that limit their password length to 8 characters.
However, the real solution is that these password restrictions are in fact not restrictive enough: If everybody would require a password to be exactly 40 hexadecimal digits, no more and no less, this would force everybody to start using password managers, and they would all be much more secure.
However, the real solution is that these password restrictions are in fact not restrictive enough: If everybody would require a password to be exactly 40 hexadecimal digits, no more and no less, this would force everybody to start using password managers, and they would all be much more secure.