One: it works because nobody is choosing
Think of a stairwell landing in a block of flats, 1998. You meet whoever is coming down. No app arranged it, and that is why the conversation is easy — neither of you picked the other, so neither of you has to justify the choice.
That's the mechanism entire, and no service has ever advertised it, because you can't advertise an absence. What they advertise is volume.
It also explains the most reported random sex video chat effect: people say they stop thinking about their own problems for twenty minutes. Not because the conversation is interesting. Because attention is somewhere with no history in it.
Which is why a free video chat beats a film for this particular job. A film wants nothing from you. A stranger waiting for an answer does, and the wanting is what holds the attention still.