The labels also invest in talent they hope will make it, spending huge sums on teaching them to play in sync, variations on playing styles, introducing them to different instruments and sounds, fitting songs to bands, practice studios, recording studios, sound engineers, etc etc etc etc. That too all costs money, and most recorded artists probably never make it really worth while, but without that support the real gems are even less likely to make it.
The problem is that from the anecdotal stories that I've heard about the music business, the RIAA and the major labels don't actually do any of that stuff. What I've heard is that most of that is done by the actual artists on their own time and their own dime. That doesn't mean that no label associated with the RIAA ever does that, it's just that none of the stories I've heard mention anything like that. In fact, most go into excruciating detail about how the labels are loathe to give anything at all away. The general story seems to be that they are billed by the music label for anything the label does for them and sometimes for anything the label could have done, even if it didn't. In particular, I remember one band complaining that they were charged a hefty fee because they didn't use the label's recording studio, and that was in addition to the fees they paid to the recording studio of their choice.
Maybe that's standard practice and I have just never heard anyone ever mention it, but I'd like some evidence that it's common for anything other than label organized boy bands.