It's because the audience that saw it on release, were probably going to like it anyway. That's generally why pre-sales, and opening weekend reviews are generally always positive. Why see it opening weekend, if you probably don't want to see it?
Contrast to the middle of the next week, where people are like 'Eh, I'll see it soon.' because they're not emotionally invested enough to see it the day it comes out.
So of course people who see it on opening night, or through Advanced Screenings are going to love it.
People who don't love the movie before it's even come out, or people who saw the trailer and went 'Yeah, looks alright...' are going to have mixed feeling about it.
'Anti-Last Jedi' would actually mean that opening reviews were weak, and audiences who saw it later, loved it.