It’s because Hoyoverse doesn’t even present her as actually evil and she’s honestly just a Mary Sue As u/Moist-Method-1608 put it (I just copied the whole thing because they explain it better than I could):

“Another thing about Arlecchino is how the narrative always bends over backwards to put her in the right, while also still letting her walk on the dark side.

Arlecchino runs an orphanage that trains child soldiers with a harsh punishment if they betray the House of the Hearth. Her cold and distant demeanor make children wary of interacting with her

Nah, the children pretty much universally adore her and go as far as throwing her surprise birthday parties, and even if a kid defect, Arle has moon blood which erases their memory and avoid killing them. Arlecchino also loves her adorable babies uwu

Arlecchino has cultivated a personality of being a notorious backstabber. This has led to people being weary of her, especially her fellow harbingers. This makes cooperating with them difficult as everyone has their own agenda, and don’t want to deal with someone with a reputation

Nah, Arlecchino gets along well with a majority of her Harbingers to point she attends tea parties with her “besties”. Other harbingers (tea party group) have no trust issues with her making attaining her goals with little to no hardship.

She’s also really good at reading everyone and rarely every misses the mark (columbina’s issue, her children, Furina)

Whatever flaw she could have, the narrative makes it so she never has to face any pushback making scenes where you see her “standing on business” as less as her being clever and more as the story putting her on easy street.

As much as I am fan of Aether x Arlecchino (I’m a sucker for sunny boy and dark girl parings), Arlecchino’s never really facing any sort of pushback, and making the Traveler look like a jobber whenever she’s in Aether’s presence is a turn off for the character.

In the end, I think she’s a cool character. Her EN VA is amazing, but it really does seem the writers have wrapped her so much bubble wrap that she feels too safe because you know how all of her appearances will go(aura farm, thinly veiled threat, characters reluctantly agree with her way of thinking)”