This is what blows my mind, how did they not look at that gameplay demo and say "this isnt going to work" when anyone can clearly see that it was not what people were expecting to see from a pillar franchise 4 months before launch on "the world's most powerful console". 90% of the internet could tell it needed a delay... how come MS didnt?
Their entire July event was centered around Halo, I have to believe that the Xbox folks have eyeballs so i can only assume they were taking a gamble that people would be so hyped they wouldn't notice the issues or they could talk their way around it. The problem is their PR isn't strong enough to sidestep that and engaged gamers/consumers aren't blind.
I agree that showing this gameplay demo was not a good idea but in their defense, regarding the positive/negative ratios on Youtube, they weren't in a Battlefield V or Infinite Warfare situation where it was clearly not what fans were expecting/wanting to see (though the graphics weren't the problem here).
But that's clear that the game took a hit between the E3 2018 reception and the gameplay demo.
COD Infinite Warfare reveal: 14% positive ratio
Battlefield V reveal : 39% positive ratio
Halo Infinite gameplay reveal : 84% positive ratio
Halo Infinite announcement E3 2018 : 97% positive ratio
I think the delay is both a combination of not enough time to finish the game (and wanting to avoid another Halo 5), dealing with the visual issues / reception about graphics (not enough time to put ray-tracing before launch) and wanting Infinite to be the best Halo ever. They probably realized that facing the November deadline while being behind schedule and having hundreds of persons working from home was not sustainable (for the team and for the game).