Usually it’s someone who didn’t want to pay for seat selection or an upgraded seat and hopes to guilt someone into giving it to them. It’s a dirty trick that makes the person who simply expects to sit in the seat they selected look bad.
Two adult women traveling together should be able to sit quietly for a few hours. It can be a real pain listening to someone else’s gab fest while trying to read or think.
Rick Steves has a trick for getting a train compartment to yourself: assume the lotus position and start chanting. There must be a clever version of that to deal with prospective seat snatchers. How’s this? “What’s your seat number? B25? Oh, no. I’m sorry but my psychic advisor gave me a list of seat numbers to avoid and that’s one of them.” Lol