I think a pretty unromantic answer would be that it's an element of rhythm in a genre that eschews conventional forms of percussion- so direction, dynamics, so on. Even a looped voice sample would, at least subconsciously, perform a similar function as a drum beat.
BUT, I think a more fun way to answer this is that in forms of industrial with little to no song structure, we are constructing worlds to inhabit while listening. I was listening to Mind Control by GO last week and realised that the repetitive nature of those songs have an effect similar to that of a painting. Rather than being a dynamic element that indicated change, progression, or narrative, the loops acted as a constant throughout the song much the same way that an ashen sky is the backdrop of a Bosch hellscape, or the glaring sun sets the tone of an Edward Hopper painting. We listen for however many minutes, taking in the separate elements of the track, sometimes other instruments like synth or feedback will tell a story over the back drop, sometimes the whole thing will be repetitive and uniform, and by the end (or even throughout) we have the wherewithal to see the "image" the song has constructed in sound.
This is my own interpretation anyway. Sometimes when the loops are more violent (see "Elders of Z" on the above album, the exception proving the rule) they are more like a killer riff, the kind you could happily just loop forever.
