You are SPOT ON with the sentiment about why the wives of some of the Royal princes are singled out for attack. It's an unhealthy, borderline obsessive feeling of involvement and identification with the lives of these men that is rooted in low self esteem, narcissism, and envy.
This type of obsession and unhealthy involvement in the personal lives of celebrities, politicians and Royals was unheard of before the age of social media.
It seems to be predominated by females...at least I have rarely seen the commoner male spouses of Royal women singled out in a similar way.
I will never, ever forget a post I read on another Royal message board at the time HGD Guillaume's engagement to Countess Stephanie de Lannoy was announced...." I find it incredibly insulting...the implication that someone LIKE ME is not good enough!"
In other words the fact that a Royal prince whom she had never met in her life had not chosen to wed a regular working class woman was a slap in the face and a rejection of herself. Personally.
The indignation and sense of personal offense of this comment made me howl with laughter at the same time it sent a chill up my spine.
Even if I have been disappointed and in a couple of cases appalled by the choices of spouse made by certain Royals...I have never questioned their right as humans to love and choose who they want.
It's about realizing that we do not own these people even if we follow them and are interested in their lives.