The British press writes about this because its' click bait.
It's the same way it was/is with Carole and Pippa Middleton. Some people just hate people because. Just because. Because they don't like them, because they are thinner, fatter, prettier, wealthier, envious, etc. You can write about these people who are disliked for just being themselves. They have never held public office they don't live off the public dole and yet they are judged (very harshly one might add) often. So you write the most ridiculous article, and people will click on it and post a comment. And this helps the advertising dollars.
The British press knows that anyone who marries into the royal family is going to be judged like this. Meghan is triple word score. She's an American Divorcee who is an actress. Actually, she is better than a triple word score. She has these family members (and friends) who are willing to line their pockets by selling stories and videos about her to an insatiable British press.
In regards to Samantha, is anyone really surprised that she is going off about not getting invited to the wedding. I wonder if she really expected an invite. What's so fun about this though are some of the comments by the Daily Fail readers. They are slamming Samantha for all she has said about Meghan in the past. They too think she is delusional.