I don't doubt Bernie knows other issues exist. However, outside of his millionaires, billionaires and Wall Street he simply hasn't shown he's got the type of understanding necessary to move the needle. Look at Bernie's LGBT issue page. It's seven points. Seven good points (although one of which is continuing a program Hillary helped start at State...), but it's not fully fleshed out.
https://berniesanders.com/issues/fighting-for-lgbt-equality/
And here is Hillary's:
https://www.hillaryclinton.com/briefing/factsheets/2015/12/17/fighting-for-full-equality/
It is far more in depth. It shows she understands the ways in which hetero privilege, transphobia, health care, aging and HIV affect our community. TO me, she shows that she better understands the ways in which all of our various traits impact our lives In short, intersectionality. Also, I don't trust Bernie to be able to build coalitions because he has absolutely zero allies in the Senate. Not a single member has endorsed him, and I don't believe he has political capital to exploit.
But, there is something that I do have to take offense with, and this isn't directed directly at you, but it's something I've seen a ton with some Bernie supporters. Please do not insinuate that those of us who support Hillary are either stupid or incapable of reading. We simply have come to a different conclusion than a Bernie support has. And that's perfectly fine! But this "If gays/AA/Hispanics/women/seniors weren't so stupid/lazy/uninformed/underinformed as to drink Hillary's Kool Aide then they'd feel the Bern" is the completely wrong line to take when you're trying to win supporters.