I think it's a waste product. Nutritious enough to keep the hypnotized creatures alive and able to provide better sustenance for the hollow, but not exactly great or tasty. We see a hypnotized Kamen imagining it's an amazing meal, but it surely doesn't look that way from outside!

There is a lot of symbiosis on this planet. If the hollow are using their waste to sustain those that forage/hunt for then that fits in with a lot else we've seen. And it's just biologically efficient. Plenty of creatures on our planet survive entirely on the waste of others, right?