Why was a royal marrying a divorcee so taboo in 20th century Britain? Edward the 8th had to abdicate because he wanted to marry Wallis Simpson. King Charles wasn’t initially allowed to marry Camilla even though they where romantically involved before and during his marriage to Diana. Also they’re was controversy over the divorce of Queen Elizabeth’s other children Anne and Andrews divorce.
In a nutshell, because divorce was not recognised by the Church of England, and the monarch was (and is) the head of the Church of England. I wrote about this before in a previous answer.