Someone will make something really good with RE one day...
RT score is not a rating of quality, it's a rating of how many selected-by-RT reviewers like the product more than they dislike the product, which is a binary yes/no.
In that sense it's very much like Steam review scores if you play on a PC, where a Mixed doesn't mean bad it means divisive and go read the reviews.
Yes a 80-100% probably equates to "this thing is really good" (or at least, it's inoffensive so a lot of people like it), but a 51-79% does not equal "bad" it equals "this is divisive. You will either love it or hate it".
Let's look at the actual negative reviews:
* "For those unfamiliar with the fabled video game series, this will feel like little more than a muddled, and somewhat tacky, zombie serial, saddled with the baggage of pre-existing lore."
* "A small deception, it anchors its most visceral component to concrete situations tied to a mystery that lacks a good hook."
* "Parts of Resident Evil's twin timelines show promise, but it ultimately falters thanks to large chunks being dedicated to a sub-standard post-apocalyptic plot that's been done better elsewhere."
* "A fter an okay opening episode, Resident Evil settles into an action-adventure slog rather than anything remotely new or scary. The complete absence of "horror" here is an egregious sin."
* "Spends most of its time desperate to justify its own existence in the Resident Evil Universe™, and none building a new story that's worth caring about."
* "There's a great Resident Evil adaptation in here somewhere, but like the zeroes scattered throughout this show, Resident Evil mostly just bites."
* "Though slickly produced and solidly acted, Netflix's Resident Evil feels too much like a generic sci-fi horror series cynically slapped with the Resident Evil branding and dusted with just enough fan service to keep the die-hards from fully tuning out."
So you got someone who hates it because they don't know Resident Evil, someone who disliked it because it didn't have a good narrative hook, someone who doesn't like it because it's post apocalyptic, someone who doesn't like it because it wasn't scary enough for them, someone who doesn't like it because it's a part of the Resident Evil universe and leans too hard into that, someone who doesn't like it for...some reason....and someone who thinks it doesn't lean into Resident Evil enough.
And all the negative reviews if you look at the actual review score and not the Fresh/Rotten are 2.5 out of 5's with 1 D. So average. Basically on the border of Fresh/Rotten.
So it's divisive.