Bernie and Liz both get along great and have gone out of their way not to be mean to one another

Because they are civil individuals who are at the upper end of society, Warren far moreso than Sanders. Sanders knows he cannot go attacking Warren all willy nilly because of how he was smeared as sexist in 2016 by the corporate media.

why do some of their supporters not follow their example?

Because Sanders' supporters are by and large the working class and have a lot to gain and lose election to election and would actually like to see their lives materially changed by Sanders' policy? People should be mad! People should be angry at the state of their lives! People should want fucking the blood of billionaires to rain in the streets.