I think they were partly unlucky - their prime time for getting really good deals was during Covid when no one was focusing on the luxury goods market.
I think also they were very unwise to push the negative stories they did - it made them look either toxic (if you didn't believe them) or sad (if you did). Neither of those is good for promoting a brand - you need happy, positive, uplifting images.
They are very impetuous and the opposite of strategic which you need to be if you want to market yourself.
And they were (still are) very delusional about their position in the world and what it could get them.
Zara is sticking to her lane - she keeps her focus tight on riding and horse related activities, and the brands that are attracted to the horsey set. She also very wisely decided to focus her main money making activities in the Australia, where she gets to be a bit special (granddaughter of the Queen) but in a casual Australian way - away from the UK paps who might be tempted to do the odd negative story about horsey rich people if they were aware of it too much.
Harry and Meghan spent their main time (when they weren't being negative about the UK and the RF) trying to be global spokespeople on big causes, or hoping for big paid speaking gigs. The problem with that is they just don't have the real world experience, or funny entertaining anecdotes to pull that off.