You haven't watched the video. The woman is arguing for veganism while the guy is arguing from the leftist perspective till the end where they finally come to common ground.
From personal experience, I've spoken to several leftists who aren't even willing to consider the issue of animal welfare because (and I'm paraphrasing here) "human issues come first". Like it's some sort of either or situation, when really the positions are complimentary.
Not sure if this is what the video is about, as I can't watch it right now.
The video is not an example of such a debate and I am not going to fuck up the algorithm watching something stupid.
I do not believe you that there are "plenty" of debates between leftists and vegans on the Internet. In fact, if I type "vegan leftist debate" into YouTube, zero debates pop up.