First of, it wasn't A tweet, it was
several tweets.
I think that part that people are most upset about was his "non-apology apology" where he basically said that it's on the LGBT community that they got offended by what he said in the past.
He could've made a 20 sec video saying "Fuck man, I can't believe I said that shit, it's fucked up, this does not reflect what my beliefs about the LGBT community are now, my apologies". Instead he made a video reminding us about how he's in a great place in life and how he's not gonna let this effect him cause it's just people that wanna be angry and negative. THEN, after receiving backlash for THAT, and "choosing" to step down from the Oscars, he apologized to the LGBT community.
Like, no, sorry, apology not accepted.
About Ellen, as disappointed as I might be, I'm not surprised. She's not exactly known for being confrontational.