Because one should never, ever, EVER say anything mean about a Senatorial colleague. Even when debating about whether said colleague is a candidate for a cabinet secretary which you, as a Senator, are expected to advise and consent about, and even when you're not actually speaking about him, but quoting others who were commenting during his (unsuccessful) nomination for a federal judgeship 30 years ago. Because that will get you quashed and told to sit down and shut up.
It has been said that rules of politeness and civility are used by the powerful to protect the status quo. I usually disagree with that sentiment, but this is certainly an example of how that is sometimes the case.
The Devil can quote Senate Rules to his advantage.
McConnell Reprimands Warren Over Speech Slamming Sessions, Calling It Violation of Senate Rule
All the Dems should read that letter until McConnell if forced to silence the entire party.
No, see, this is how Trump and his Republican coterie are doing away with annoying political correctness…wait, that doesn't work.
And they call the left snowflakes <snort>.
I was going to add a snarky comment about how we've always been at way with EastAsia, but for kids in high school that's actually true.