Oh come on, those Bromptons are a fashion item as much as they are a transport device. Don't play that game with me!
Really? Are you implying that all cyclists are perfect and never cause issues for their fellow commuters? Perhaps you'd like to tackle the issues instead of resorting to simplistic insults?
I know how touchy cyclists are about criticism these days, and like to film everything they don't like, so perhaps one or two might like to observe how some of their fellow cyclists behave on platforms and trains. I witness on an almost daily basis folding bike owners (not all Bromptons by the way, hence the generic term) arriving onto busy commuter trains, leaving their unfolded bikes in doorwells whilst other commuters try to board while they sort themselves out, get a seat etc, then proceed to start to fold up their bikes. So having had opportunity to fold bikes on the platform, they have instead chosen to wait until boarding before completing the task. So in the light of this, it is not unreasonable to ask owners to fold their bikes prior to going through the gates, thus negating the issue above. If said owners chose to stand to one side on the platform to fold their bikes, then fair enough, but some don't.
So if a TOC, or member of station staff regularly sees this behaviour and decides for the benefit of all passengers to ask owners to fold bikes before entering onto the platforms, this is a reasonable course of action. If this causes a minor inconvenience, and it is a minor one, to cyclists then so be it. I'm afraid the railways are there for the benefit of all.