I think one of the reasons autistic people get flagged as lacking empathy is that empathy with people who are fundamentally different from yourself is hard. This goes for both autistic, and non-autistic people. I’m going to speak fairly pop-scientifically from here on, but this is a field tangentially related to mine, not my own, and I’m not going to attempt to bust out the big academic guns on this answer. To a large degree, you experience empathy by projecting your model of yourself onto other people, and determining how you would feel in their circumstances. I’m not claiming this is the only factor at play, but: autistic people are quite fundamentally different from non-autistic people cognitively, with all that entails in the domain of behavior, priorities, emotional responses to various stimuli, likes and dislikes, communication, and so forth. If an autistic person attempts to use their model of themselves to understand a non-autistic person, it’s largely going to fail. But that’s largely how empathy is supposed to work.