I think this is what people object to. From their own website it says, that as well as their charity stuff, “they value the ability to earn a professional income, which in the current structure they are prevented from doing.” But they’re not actually walking away,They still want to do royal engagements (when it suits them)
Nobody else has been allowed to do this. Edward and Sophie eventually had to give up their other work as there was a conflict of interest between making money from that and being full time working royals, which they are now. Zara gets money from sponsorships etc but she has never been a working royal.
They plan to give up money from the Sovereign Grant, but this is only about 5% of their income. Most of the rest of it came from Charles but whether he will still be prepared to pay it now they are planning to make money themselves remains to be seen.
They also want to keep FrogmoreCottage, presumably rent free even though they’ll be in Canada as well, they expect their security paid for as well. While their security has been expected to accompany them on overseas tours and holidays, they’ve never been expected to spend half the year in Canada before.
If they were actually giving up everything and going off to live quietly somewhere off their own millions, that would be fine. But it’s not what they’re doing. What they’re planning to do is CFery and they didn’t even bother to tell the queen before putting it on their Instagram.