I think it makes most sense to look at the "I've used it, wouldn't use it again" rather than "I haven't used it, not interested in using it". Those breakdowns are quite revealing in fact for both React and Vue.

Do they say Ember is bad, or that they just haven't used it and have no interest in trying it?

They provide a 2d grid for positive/negative sentiment crossed with have/not used. So there's a quadrant of negative sentiment + have not used that Ember dominates the corner of! It's a weird set of beliefs to hold - hating an unknown - and even weirder to care enough to fill out that part of the survey.

I mean. It’s a poll. Its express purpose is measuring popularity at a point in time. I can’t imagine what else would be expected.