It's a question of popularity

Prince Charles is the longest-serving heir apparent in British history, but he hasn’t enjoyed great popularity with people since more private details about his marriage to Diana, Princess of Wales became public knowledge. One 2018 poll showed that the popularity of the man who is next in line to the throne is decreasing, while a recent Express poll revealed that people would prefer that other royals ascend to the throne. Harsh, we know, but it’s not completely without cause. These are the reasons why the British aren’t excited by the idea of Prince Charles becoming their new king.
They favour Prince William and Duchess Kate

Prince William, Duchess Kate, and their three children are adored in England. In fact, a survey by BMG Research reveals that nearly half of the British public wants Prince Charles to step aside and give the throne to his oldest son when Queen Elizabeth II passes away. Prince William and Duchess Kate have now been married for nearly a decade. The Atlantic calls them a “fairy tale,” with their picture-perfect family and their distinct lack of scandals. Plus, Prince William and Prince Harry are the most liked royals “since records began,” according to the Evening Standard, so, it makes sense that people want to see their most liked royal on the throne. That said, Prince Harry’s popularity may have taken a bit of hit since he and Meghan “stepped back” from their royal duties.
An affinity for Princess Diana still reigns

Princess Diana once said that she wanted to be the queen of people’s hearts, and that very much proved to be the case. It’s also a big reason many people don’t like her ex—they still haven’t forgiven him for how he treated Diana during their ill-fated marriage. Prince Charles publicly admitted that he started having an affair with Camilla Parker Bowles in 1986 while he was still married to Princess Diana. He also treated Princess Diana poorly on a number of occasions. The public, who is still protective of Diana, seems to be unwilling to move past Charles’ past offences.
Check out these “facts” about Princess Diana that just aren’t true.