Why are regressive taxes considered heaviest on low income taxpayers?

It's considered heaviest on low income taxpayers because the tax payable can be eat high through their income adding to their budgets or expenses

Explanation:

First let's know what Regressive Tax mean;

A tax is regressive if every member of the society has an equal burden of paying, despite wealth and income levels.

So if everything member of the society pays at same rate, the wealthy (millionaires) won't be equally financially shaken like that of a petty trader or low income earner.