This is a classic case of inappropriate or inaccurate borrowing of a word!
Once upon a time consumption meant 'wasting away', but in the context of tuberculosis, not shopping.
Of course these days consumption is still a kind of wasting, but not as life-threatening!
A consumptive consumer!
Consumerism is the modern habit of wasting money on wants rather than needs.
Compare: consumptive and consumeristic.