The vast majority of money-earning musicians don't earn anything significant from album sales, they have to rely on live gigs and merchandise sales. This shouldn't come as a surprise.
And a lot of musicians don't make anything, or are actually losing money. But they keep doing it for the love of the art.
Would I like to see these talented individuals properly compensated? Hell yes! But between predatory record labels and the sheer vast number of people out there also producing music, it's not easy to break through.
And remember that not every project is a rock band. Think of an ambient, experimental artist creating calm music for home listening and an adult audience - those artists won't fill any venues or impress their listeners with colorful t-shirts. They rely on album sales.