The real problem is exactly what you say: decreasing monthly expenditures on music. Increasing usage will depress per-song revenue but per-song revenue is irrelevant; what matters is absolute revenue.
Artists don't (or shouldn't) care about getting non-zero remuneration at the margin; they should care about getting non-zero remuneration in absolute terms.
Artists don't (or shouldn't) care about getting non-zero remuneration at the margin; they should care about getting non-zero remuneration in absolute terms.