Apparently Frogmore was offered as an alternative to Windsor castle because Ginge and Cringe insisted from the start that privacy was of thhe utmost importance and what they wanted most, and Windsor couldn't provide that. The queen said there was too much coming and going at Windsor (I believe it has grace and favour apartments) and privacy would be impossible for them so she offered Frogmore because it's so isolated and easier to keep secure and private. Harry accepted on the basis that it would be renovated and modernised to their taste.£2.5 million later the gruesome twosome changed their minds.
Maybe megs fears the ghost of Wallis Simpson, who is buried there, will haunt her and wag her finger at her
"Honey child did you learn NOTHING from my experiences !"