I think the argument people are making is that if you’re in full possession of all the facts etc, it could be considered selfish not to have one if you have the financial means to do so in order to help protect the general population.
I completely agree that the NHS guidance says that there’s no need for people who aren’t in an at risk group and are otherwise healthy to receive the vaccine. I disagree with the way they’re communicating this, but I imagine it’s not lazy/by chance and that they have studied the impact of specifically targeting at risk groups with their policy statements vs something more broad brush (even with the caveat that some people will have to pay).
The information is out there for ANYONE to access, but like you and @meowington have pointed out there is no driver for people to proactively consider having the flu vaccine unless they’re at risk.
The pro vaccine chat on here has (I think) been aimed at filling a void that clearly exists. No, not everyone in the UK will read it, but if you have, and haven’t previously considered having a flu vaccine hopefully the rationale is, at least a tiny bit, clearer.