*I think that Meghan just couldn't accept that she wasn't the "star" of the family - and also that greeting people and making them feel comfortable was part of her "job" as a working royal. Meghan thought, I think, that she would command superstar celebrity status in the UK, in the same way she'd wanted to get in the US but never managed.
She was massively popular when she married Harry, but she was never more popular than William and Catherine and didn't like it.*
Looking objectively at the four of them, Meghan, in my view, is the most polished followed by William then Catherine and finally Harry. Meghan is the best most natural public speaker, she also has great sense of style and is beautiful.
If the Royal family was a traditional PR or marketing company , she would have been groomed to be the next CEO. Kate does not have the same speaking skills for a global stage and yet she is the one who will become queen. Perhaps Meghan thought she was entering a meritocracy and her talents would be fully utilised, but the monarchy definitely isn't a meritocracy. Her role was to slowly fade into the background of the royal family, as Kate rose to become queen and understandably she didn't like it.
I think if she had understood more about the royal family before marrying, she would have bailed like Cressida and Chelsey before her. And then merched her almost royal status back in Hollywood.