"If it was why I was quitting, I would have not come back this year," she told Savannah Guthrie in an exclusive interview on TODAY Thursday. "I really did think about not coming back, because it was devastating. It started with attacks on me and attacking everything that I stand for and believe in and built my career around ... I am a kind person. I am a person who likes to make people happy."
She added that she had "no idea" there there were problems behind the scenes until reading about it in the media, and disputed any assertion that she should have known what was going on.
"I don't know how I could have known when there's 225 employees here and there are a lot of different buildings," she said. "Unless I actually stayed here until that last person goes home at night.
"It's my name on the show, so clearly it affects me, and I have to be the one to stand up and say this can't be tolerated," she said.
The show has also suffered a ratings decline after its most-watched premiere in four years, in September, which opened with a lengthy apology from DeGeneres. Following that peak, the show lost more than a million viewers, averaging 1.5 million viewers over the past six months compared to 2.6 million for the same period last year, according to The New York Times.
But DeGeneres said the lower ratings also were not a factor in her decision to wrap up the show. Savannah noted that while ratings have been down for every talk show, DeGeneres' show has seen a more steep decline.
"It's more for this one because we had further to fall," DeGeneres said. "And everybody else was at a lower place, so they didn't have as far to fall. To be honest. I mean, that's the truth, we were very, very successful.
"As you said, everything in television is down. It's got nothing to do with why I'm leaving. If I was having fun, I would do this show with nobody watching. So it's got nothing to do with that."
The controversy brought back memories of DeGeneres' sitcom being cancelled after she came out as gay in 1997.
"My therapist is like, very few people go through such huge public humiliation twice in a lifetime," she said. "How can I be an example of strength and perseverance and power if I give up and run away? So it really is one of the reasons I came back. I worked really hard on myself.
"And also I have to say — if nobody else was saying it — it was really interesting because I'm a woman, and it did feel very misogynistic."
The backlash she faced had a profound effect on her.
"No, I'm not bulletproof," she said. "And no, I don't have thick skin. I'm extremely sensitive to the point of it's not healthy how sensitive I am.
"When something is coming back at me that I know is not true, I guess I could take one or two of those shots, but four months in a row took a toll on me."
DeGeneres taped an emotional monologue on Wednesday, set to air on Thursday's show, in which she thanked her fans for all their support over the years.
"The past 18 years have changed my life. You’ve changed my life," she said. "I am forever grateful to all of you for watching, for laughing, for dancing ... sometimes crying. This show has been the greatest experience of my life and I owe it all to you. Thank you. Thank you. Thank you."
Filming it reminded her that doing the show "has been the best experience of my life," she told Savannah.
"I'm most proud of going 19 years on this show," she said. "That is an accomplishment. I'm most proud of the people who work here who have stuck by me and who have supported me.
"I'm proud of the kind of show that we do. I'm proud that we are funny. I'm proud that we are helpful to people."