Because it's not just money. It's time and money. You can have lots of money and nice things, but if you don't have time to raise your kids, you can't do it. And if you had the time, you wouldn't have the money.
Second, it’s hard to find a good nanny. Parents live in fear of not getting a good one, having something go wrong and need to scramble for a replacement without missing too much work, etc.
It’s possible but it’s not going to move the mainstream averages because only like 5% of the population does that. If we want to materially change national averages, we should be talking about government daycare filling in the gap before public schooling starts around the country.