The controversial answer might be that the wealthier brackets are more likely to be holders of financial investments, and the tax code seems to clearly benefit

The controversial answer might be that the wealthier brackets are more likely to be holders of financial investments, and the tax code seems to clearly benefit wealthier groups because the tax code is influenced BY the wealthier class through lobbying and the sorts. If I had no context of the situation, I would see the lower % as a way to incentivize people to invest their money in things that would fall under capital gains.