Because we already have the former and we don't need the latter.
A carbon tax with a dividend doesn't make life harder for lower income people, because they already have below-average energy consumption (wealthier people have bigger houses that need more heat etc.) and as a result the dividend would be larger than what they pay in tax.
But you still want them to have good incentives. If they can use the dividend to switch to solar or buy an electric car, you want them to do this, because that's the whole point.
Meanwhile there is no reason to charge profit-seeking enterprises more than the true cost of their usage, because all that's doing is inhibiting economically productive activity. Aluminum smelting uses a tremendous amount of electricity, but what you want is to cause them to switch to non-carbon electrical generation, not to shut down operations.
