A wealth tax encourages spending, for example on private school tuition, SAT tutors, and other things that can help your kids. It only hits the money/assets you have left at the end of the year. It's also likely unconstitutional in the US (despite being backed by an HLS professor, who you'd think would know better). Andrew Yang is backing a heavy consumption tax, which would be used to give cash to all adult Americans. This would have the opposite effect, since it would encourage savings over spending.

To my knowledge just giving people who need it money doesn’t encourage them to save it, but rather to spend it on what they need, which actually stimulates the economy. This is far more beneficial than leaving it as idle capital or in a savings account.

You're right that the propensity to spend is higher among low-earners, so if you're trying to stimulate the economy it makes sense to allocate there (all other things equal). But my point was about the futility of trying to use a wealth tax to cut down on generational transfers of wealth/advantage. If you tax wealth, that encourages people to spend instead of save. And if their concern is keeping their family in the top 5%, 1%, or .1%, there are plenty of ways for them to spend it in order to achieve that end.