I agree with @Greenpolkadot that MM probably had no idea how all-compassing royal life would be and how intrusive and nasty the press can be either.
I live in the US and I can honestly say that the average American knows little about the royals aside from their names (of the well-known ones), why would they, it's a different country? Also, MM really WAS a minor actress who didn't garner much public attention. I live here and I had no idea who she was when their engagement was announced. Only "Suits" fans would recognize her name!
They're not happy so they're stepping down as senior royals. Fair enough, I hope they have happy, successful lives.