The only reason I can see that it keeps getting renewed is that ITV wants to keep Simon Cowell happy for as long as BGT still pulls in the ratings. My guess is the two shows probably come as a package.
If ITV told him they didn't want X Factor any more, he could maybe threaten to take both to Channel 5 or Sky.
As previously stated, BGT has been renewed till 2024 while The X Factor has only been given one more year.
Spencer and Cando gave kudos