I would more than happily take a day's annual leave to stand up and give evidence against anyone who considers this highly antisocial and easily avoidable practice acceptable.
Just use headphones. It is not in the slightest bit hard, and they are dirt-cheap.
But the reason I responded strongly to the OP was that he did it deliberately to annoy others in the hope they would move - and that is grossly antisocial and has no place in any public space of any kind. You ask nicely, and you accept refusal gracefully. And if it's that important and that train doesn't have any seats together, you take a different one.
FWIW my personal policy is that I will move if I am asked nicely, but I will not move if I am asked rudely or with any kind of self entitlement or complaint, provided the offered seat is acceptable (i.e. enough legroom for me to physically fit, and not a "window blank" seat). The exception is that I will not, unless instructed by staff, move from my reserved seat into a seat marked reserved because I could later lose it to the reserver (most trains don't show different reservations separately, so "reserved to Manchester Piccadilly" may mean several sets - I've been caught out by that before!)
Given the attitude shown in the OP's post, I suspect they didn't ask nicely, and so people didn't move.