Well if you want to argue semantics...
"Main output, secondary input" is not what MOSI means, it's just made up bullshit to be politically correct. Everyone knows it's Master out, Slave in, so were the words "master" and "slave" banned or were they just changed? What is the difference?
The meaning of BAN is to prohibit especially by legal means; also : to prohibit the use, performance, or distribution of.
They aren't banning it anywhere on their forums or comments, that I am aware of. You could say banned internal use though.
Its their own private business, if they decide to call a banana a vegetable, they are entirely entitled to do so, regardless of how wrong or stupid it is. Hell they could require their employees to all dress up as elves during work.