The difference between the charity work done by the BRF and H&M is that H&M must make the charity work pay them. The RF do not take salaries from their charities, they get money from the sovereign grant and duchy of Cornwall etc. H&M have no choice but to take a salary from their charitable endeavours if they are to succeed in the long run.
The Spotify deal was canned without full payment, Pearl was canned, the Bench proved Meghan doesn't have original ideas (the Boy on the Bench (nifty bit of plagiarism)), Ms Haversham, Elephant, Look to Lead...all look very unconvincing. Spare/the docuseries/Oprah were simply car crash fascination successes, and that cup has run dry.
So they have no option but to start either earning serious money, wait for the windfall inheritance or take salaries from their charities.
Having read a while back the book 'meet me at the lake' (it's forgettable) I can't see it being a great success. I felt like I was back in the 2000s with all the Tig like lifestyle nonsense. No real connection to Harry's loss of his mother, as it's the heroines mum who dies in her adult life. Very Hallmark territory.
Harry and Meghan are not philanthropists. They are not wealthy enough to give away their own money.