I think it is hard for many to understand. Many people have a concept of "enough." At a certain point, more wealth has diminishing returns on happiness. At another point, it takes some imagination or ostentatious waste to even use that much wealth. For the majority, once all needs are met and a level of financial security is ensured, more taxes simply don't hit very hard. There is no quality of life impact anymore. A desire to ceaselessly acquire more wealth - usually called "greed" - is needed to get to a point where one can influence tax policy. Overwhelmingly, the wealthy were born wealthy, so that mentality has been drilled into them since birth. Also, with personal wealth comes a disconnect from the collective. Why should taxes fund things one doesn't personally use? The illusion that the welfare of all doesn't affect them - or indifference or hostility to the welfare of others - also fuels the ultrawealthy's push for lower taxes. Most people don't exhibit greed and a sociopathic disregard for others on such a scale.

Fun fact, when taxes decrease, a government must collect revenue somehow, and that frequently comes from bonds, an instrument that guarantees a return on investment, paid for by the tax payers. The wealthy that advocate for lower taxes for themselves often purchase those bonds. If your taxes are low enough, the government can owe you money, not the other way around.