I can assure you that if the labels could "manufacture" success, they would do it a lot more. There's no quota system, and it's only slightly zero sum. (If it was zero sum, the music industry would be doing *much* better right now.)
After all, the labels do *lose* money on probably 80-90% of those they pick up. If they could manufacture just the successes, they'd drop the rest. It would be like a book publisher trying to only publishing best-sellers. Remember, we don't notice the artists that the labels spent a million or five to promote, but just dropped out of sight. We probably never even heard of them, they're forgotten so fast and a million dollars doesn't actually go that far. It is, however, enough to get some traction if there's traction to be had.
I suspect your mistake is assuming that talent (or any other single quality) is correlated with popularity. It's not quite random, but it's pretty damn close, although people are payed millions of dollars to make guesses in the creative arts that are only slightly better than chance.
What promotion does is get the artist in front of enough faces that if they have "it" (and nobody knows what "it" is), then they can succeed (as opposed to being liked, but never hitting the critical mass where people like your music because other people like your music - music is social).
It's fun to be cynical, but the truth is that in the creative arts, there's always massive insecurity because people's livelihood depends on predicting what cannot be predicted. You spend your entire life trying to control when you don't know what you're doing. Luck grants you a streak, and suddenly you're brilliant. Hit a dry spot, and suddenly you've "lost touch". No surprise it eats away at the psyche.
Sorry, went off topic there.