That's probably part of it - also seems like if they're mostly doing a pressing rather than a plucking action it would result in this sound?
Why do the strings need to be muted? Is there so much resonance that playing quickly would produce indistinct humming?
Probably a factor, but I think it’s more for ease of use with all those strings, so that incidental contact isn’t producing sounds, along with the pull off energy when releasing notes. You do a lot of subconscious muting when playing a guitar for example.