I think this is a fair question ie what motivates people to criticise her so much.
Ever since I was a little child (pre-internet!!) I've been baffled by the dye-in-the-wool royalists. The ones who turn up at wedding decked out in Union Jack suits, the ones who have all the memorabilia in their homes, the ones who queue up in the cold and rain to see them pass in a car etc. I understand the historians, but not the fandom. It's different from pop stars or movie stars in that at least they have some creative output to latch onto, something that might resonate. I can only think that something resonates with these fans, enough to push them into sycophancy.
The mirror image of that, you could argue, is this equally passionate critiquing of Meghan and Harry. Except, I critique (and have done since the very first hypocritical lecture over zoom during the pandemic, where she - a woman who came to riches and prominence only through marriage - tried to tell young girls that they're enough if they just try hard at school) Meghan Markle but have never, not even as a teen, stooped to any level of fandom. Never had a poster of a person on my walls, even! So I don't think it's mirror images of the same thing.
I think with Meghan it's that she thinks she's pulled the wool over people's eyes, including Harry's (and possibly her own) and yet there are many women who recognize her for what she is because we know women like her in our own lives. Plus a really base tabloid-esque wish to see 'justice' ie the wool being pulled from people's eyes. She's a chancer, that's obvious to anyone with eyes. There's nothing wrong with being a chancer, we all have to make a living somehow and women sometimes need to be extra-resourceful. But what sticks with MM and her ilk is not owning it. Lying, duping, pretending she's something she's not. I have never criticised MM for hustling; I actually semi-admire her for it. But my goodness the hypocrisy and duplicity and sanctimony. Nobody likes a bullshitter, and sadly for MM they ALWAYS get found out eventually.