This isn't uncommon or new. Many states allow for tips to offset wages, even if wages fall below the minimum wage. Some states even have a separate minimum wage for tipper workers that is below the standard minimum wage. If you want to blame someone, I suggest looking for the actual culprit and not a law-abiding company. This has little to do with Instacart and everything to do with state wage laws.
It may be legal for instacart to take the tip money but it’s their decision to do so and they deserve the blame.
It’s wrong because the people paying the tip generally believe it goes to the person providing the service, not to the company. And it subverts the purpose, which is to incent and reward good personal service.
So the company ends up screwing their workers, deceiving their customers and disincentizing good service.
Legal, but wrong and stupid.