"Despite several public statements from Harry that he now sees his future in the US, he and Meghan decided to reimburse the Crown Estate for the cost of renovations in a deal which included leasing Frogmore Cottage for an unspecified number of years.

The couple claimed that it would mean 'their family would always have a place to call home in the United Kingdom' as they pursued lucrative commercial deals abroad."

First of all, the media and the Lumps are stating Frogmore Cottage was a gift from the Queen, no, the propery was given for "their use", meaning they were still responsible for the lease and the upkeep, etc. I'm sure in the agreement, there are provisions spelled out and I'm sure in there are provisions spelling out conditions concerning not renewing said lease or revoking the lease.
If my sister or a friend has a car and gives the car for "my use", I still have to take care of the car, maintenance, fuel, upkeep. The understanding between the Sussexes and the Crown Estate was that Frogmore Cottage would be their "home in the UK and repayment of the renovations was based on that fact..this is their UK home. Their statements concerning that the US is now home, will never return to the UK because of the racism, blah, blah, broke the good faith agreement.
The Crown Estate, as the "landlord" has/had the right not to renew the lease and you know there was communication between them and Charles. I'm not going to guess if it was first Charles or the other way around, but both parties were involved.
Concerning repaying the Sussexes the renovation money, I don't know about the UK. Here, if your lease is not renewed and say, you made improvements to an apt. or rental home, you're out of your money. For the little time that Harry and Meghan actually lived at the place from after their marriage until now really is not calling it their home in the UK. They just want it so they can use for Netflix filming. Oh, and maybe they didn't ask for permission to film at Frogmore Cottage...don't know, just throwing that out.