Not every group has a coterie of insanely rabid fans to follow every thing they do and buy out their every one of their concerts. Groups like that are rare and far between. Some performers cannot even do live performances. Others the cost of performing far exceeds the income possible to be brought in. Recording sales provides their income.
What you are saying about income is the exact opposite of what my friends in the industry have told me. They all say they make nothing off album sales, and that their tours are where they make the money.
I think Coldplay is another example.