Of course they wanted the cash. How else are they going to earn their money whilst living a quiet and peaceful life? They're hardly going to keep up their lifestyle working small local town jobs are they.
If they stay = They're just leaching off the taxpayers funds
Now they've left = Look at them. They just want to make money
That's literally never going to be needed. Megan would be worth a few million from suits alone.
Princess Diana left circa 20 million in a trust fund to William and Harry, to be given to them aged 30, back in 1992... two decades of compounding 20 million gives quite a nest egg in itself! She also left about circa 20 million in jewelry etc.. too.
Prince Charles is entitled to an annual income from the Duchy of Cornwall, a portfolio of mostly land/property investments worth circa 1 billion - even with low yields that gives him 22 million a year - that pays for both his households and those of his sons... Harry doesn't even need to touch whatever his share of the 20 million invested in 1992 is now worth.
We don't know how much of Charles' income gets put aside into personal savings each year or indeed how much of that which he diverts to William and Harry gets invested as personal savings/investments for them either - but Charles essentially has an 8 figure income and both William and Harry have a 7 figure income stream to pay for their respective lifestyles from that alone.
There is private wealth too of course - the Queen has her own private investments/property etc.. (outside of the Duchy of Lancaster - the Duchy itself also pays her 20 million a year and this is just private income for her - her household stuff gets covered by another income stream from the Crown Estate), her personal portfolio is likely well into the hundreds of millions. Note the Queen Mother left the Queen between 50 and 70 million in her will, various members of the Royal Family will have several million invested etc.. and the Queen gives substantial gifts to her kids, grandkids etc.. all her children have been given large houses etc.. + they and other relatives are given the use of palaces or apartments/other homes in and around palaces etc... Would be surprised if she hadn't passed on money too.