Probably because your wife wasn't there in the trenches like you were. You created the wealth, she just benefitted from it.
Please note that I'm not ragging on women. Children of rich families would also probably have the same attitude, regardless of gender.
Honestly, I'm surprised that there aren't a few therapists who work exclusively with founders - I'd honestly love to see a VC firm with a therapist on staff for its founders.
It seems like it couldn't possibly produce a dynamic that's much different than say corporate HR. Wherein the helping hand extended to the employee is always beneath that of the one that's protecting the company.
But, maybe that's just me exposing my rank cynicism, which by some measures is a personality flaw in its own right.
Maybe better if they could just refer some independent therapists who have experience with founders.
I think you can pour so much of your energy and focus into this vision of the goal you need to complete to feel fulfilment/happiness that it blocks out the depression, you're too busy to feel down and it will fuck up your plans and your goal to give into it, that's for other, less successful people (not my view, just what one tells oneself).
Then you get to that goal or aim and realise it doesn't make you feel the way you told yourself it would at all, maybe you feel a moment of satisfaction but it's probably very brief. Then you realise the beast of financial insecurity and social failure has stopped chasing you and that drive to override your mental state disipates, then you're alone with the underlying problem, the lack of any meaning to it all.
Sorry if that's not the way you experienced it but I thought I'd bounce the idea around. I hope you find a way to work to some peace with it.