I imagine it's because if the conversation is terrible you're still stuck together for potential hours. It's high risk medium reward.
I've had many fantastic conversations with people on planes and few meh ones, it's deffo worth putting a bit of effort in.
where is the risk?
I would just put on some headphones and read in that situation
I always have some noise cancelling headphones where ever I travel, great for reducing the noise of screaming kids and people trying to facetime