[mecha_ghidorah]

The poor definitionally spend a higher percentage of their income on just about everything because their income is significantly smaller

[bryanlarsen]

True, that is the primary effect.

But it holds even if we calculate as a percentage of expenditures rather than as a percentage of income.

The poor tend to spend more of their money on hard goods and the rich a higher percentage on services. And of course goods are a lot easier to import than services.