He cares a lot more about the future of the Democratic party than Hillary. Her supporters are doing the best to shrink the party. Bernie brings a broader coalition, as evidenced by his superior showing in general election polls.
Ah, yes... Bernie's "broader coalition." The one that's getting over 3 million fewer votes than Hillary is. But, it is true. Bernie has a diverse set of supporters. From the blindingly pale to the merely pasty, from the black Irish to ginger daywalkers... 18 year olds, 19 year olds, even 22 year olds! Truly, Bernie is building a colorful millennial whitebow of diversity.