I think you're thinking more of public domain, which has no copyright attached and can be used however you'd like.
I think you're thinking more of public domain, which has no copyright attached and can be used however you'd like.
As far as I understand, MIT-style license requirements can be satisfied by comments in the HTML or CSS whereas Creative Commons Attribution style licenses require the attribution to be visible to the end user.
Either way, I don't see what the issue is with designers not wanting to attribute.
https://creativecommons.org/licenses/by/4.0/
"You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use."
It's worth nothing that CC-BY-SA is incompatible with the GPL and similar licenses, so you would not be able to compile the images from Material Design into a GPLed app. You can include them with a GPLed app and load them at runtime, though.