I see no reason why Prince Edward wasn’t allowed to make programmes about The Royal Family for Ardent Pictures
He did - "Edward on Edward", "Windsor Restored", "Crown and Country", etc.
Trouble is he couldn't make it pay, and the rot set in when William went to Uni and, with film crews having agreed to back off, his crew were found to be still poking around for titbits
What with that and Sophie's company failure / "fake sheikh" sting, they were paid off with yet more funding from the Queen, one of the biggest homes of any of her children and an expectation that they'd forget the commercial stuff, concentrate on royal duties and generally shut up