Another way to look at it, e.g. for income tax - if we take the same % (e.g. 30%) and think in terms of absolute numbers - for poor it is anyway a small amount,

Another way to look at it, e.g. for income tax - if we take the same % (e.g. 30%) and think in terms of absolute numbers - for poor it is anyway a small amount, but for the rich the abs number might be so big that it becomes uncomfortable to just give such lump sum to government, especially if you don't like how gov spends it - so the incentives are much higher to optimize/avoid your taxes.