Also: Please correct me if I’m wrong but I would guess that quite a few owners of indie labels also have other sources of income in order to make a living…? I.e. a dayjob.
The vast majority of indie label owners are toiling away by day to fund their passions. If you are a successful indie label you are likely investing a lot of your profit back in to sign and put out more bands. Some are able to run a profitable record label along side a more 'traditional' business like a record store, recording studio, or being in a fulltime touring band.