As far as whether or not HAM can afford their lifestyle, for them, that's not the real issue. It's that they believe that they shouldn't have to. People should be falling all over themselves to give them things.
Harry was born into that to a certain extent. His every need and want was provided him, probably at little to no cost or effort.
For Meghan, that's part of the 'Entertainment mentality' and the reason behind all those clothing designers, car companies, etc etc giving things to celebrities who could easily afford to buy them. And the bigger the celeb, the more (and better) companies want to give them 'freebies'. For the companies it's about the exposure of their brand on someone others want to emulate. For the celebrity it's more validation that they are that person.
Harry expected all doors to be open to him based on his birth. Meghan was in Hollywood long enough to see the 'perk of freebies' in action and to absorb the belief that the more and better freebies one gets it means that you've 'made it'. And to envy those who were in that top tier of freebies. She expected marrying H to unlock that vault for her in the UK. It wasn't allowed to take 'freebies' in the RF and the RF wasn't unlocking the royal vault to her satisfaction so she wanted out, thinking that her marriage would put her in that top tier in her chosen world, Hollywood. It didn't.
HAM still want those freebies and at this point, they still expect them. And happily accept them when they're offered. Because in their minds it's their 'due'. I think the backlash comes when it becomes clear they don't believe they have to repay 'in kind'. That mentality is another reason why the MIGS will be pushing hard against them being made 'faces' for the RF in any capacity.