I think it's really important for men and women to understand that sex is just wired differently in our brains.
For a man (generalising ofc, but for the sake of this post I won't nuance everything I say), sex works like this:
If they are stressed, sex is a stress relief
If they are sad, sex cheers them up
If they need to unwind, sex helps them do so.
If they feel neglected, sex makes them feel important and valued.
Therefor the willingness to have sex is more present on a day to day basis. Sex is the remedy to most of their emotional and physical needs.
For a woman, it's completely different. Every emotional and physical need is a barrier that blocks their desire for sex.
Sex is not the remedy. On the contrary, when they are stressed/tired/touched out,... sex is another chore. Another ask.
Sex is not the solution for how they feel. It's one more thing they need to take on.
Only when a woman is free of stress/anxiety/..., does her willingness to have sex appear. And only then does sex become something she can actually enjoy, rather than it being a chore.
So take this theory and now look back at what the OP is saying.
Yes, before children and career and responsibilities his wife was much more willing to have sex. Of course she was. She had far fewer barriers and far less stress and anxiety.
Right now she has so much on her plate that she finds it hard to reach that stress-free point where she actually feels a desire to have sex.
The answer to that is not to pile more duties and responsibilities on her and make her feel like her low sex drive is yet another problem she needs to solve.
The answer is actually quite simple. How about you, OP, become her partner on the quest to lessen her stress and mental load. How about you care enough about how she's feeling - not just when it impacts you because you won't get laid but because you care about the woman you're spending your life with - and you realise that her low libido is an alarm bell going off. She's tired, exhausted, overworked, overextended and she needs a break. She needs help.
Now, don't take this as me saying you're not doing anything at all. I don't know your situation and I don't know how much you contribute to the household you're a part of. I'm saying that despite your efforts, it's clearly not enough because one of you is clearly just drained.
And maybe, just maybe, if you start caring first and foremost about how your partner is doing, not because you'll get transactional sex out of it but because you genuinely care and want to make her life better, maybe you'll start seeing her wanting you again.