"So, the labels charge the bands for everything they do for them? So why do they then also take 90% of the income?"
Because, as the article explains, many bands (presumably most of them) never pay back what the label invested. If TMJ never earns them a penny, they have to cover their losses with those who do.
According to the article TMJ probably earned the label back all the money they lent them, but from a different revenue stream. The loan doesn't get paid back from all the money the band generates, but from a small percentage of it.
Let us say that an album sale makes $6 for the label and $3 for the band, then the label first takes the $6 and then also takes the $3 to pay down the advance. So even though that album sale in effect gave the label $9 in revenue, they only decreased the loan by $3. So in this example the losses from a 90k$ advance will be completely recovered after 10k sales, but the band will still 'owe' the label until they've made 30k sales. So just because a band still 'owes' a label hundreds of thousands of dollars, that does not mean that the label lost that money.
The labels, are, in effect, lending the money the band needs to start and promote itself. If you give me 100K today and I give you back 100K three years from now, I won't expect you to think we are even.
However if I gave you 100K today to start a company with the condition that I get 60% of every sale you make plus you still have to pay me back the 100K out of your 40%, then it is certainly possible for me to make out very well from the deal even if you never actually manage to pay me back the full loan. At what point we are considered "even" is of course up for debate.
The $100K are used to promote the product, so it is just an investment for the label -- which may be eventually fully paid from the band's money. It looks like a sweet deal to me.
Because, as the article explains, many bands (presumably most of them) never pay back what the label invested. If TMJ never earns them a penny, they have to cover their losses with those who do.