The same people who taught William about the Duchy’s financial portfolio could have educated Harry about financial issues, as well. Who knows, maybe they tried.
Maybe Harry thought he would be handed a large estate when he married and not only a job and a flat in one of the Royal residences. After all Anne got Gatcombe to raise horses with her then husband, Andrew got Sunninghill, which he could sold for several millions and then could lease the Royal Lodge cheaply, while Edward got Bagshot Park and William Anmer Hall. While Harry was offered app. 1 in Kensington Palace which he exchanged to a cottage on the grounds of Windsor Park. Not that I say this wasn't enough but still it is something else than Gatcombe Park and it never was his to be completely. Maybe Harry "thought" that Charles could pay part of his mortgage on their US house as part of his "inheritance". And I guess Charles would have given him more if he had been king already. But explain that to Meghan.
Btw - there was a clip on the vid offers on my facebook about how Harry and Meghan did something "wrong" during their first appearance on the queen's garden party shortly after their wedding, so Charles ordered Harry to take her home?? Did you read someting about that?