I suppose it’s inevitable that if you sell advertising space, sometimes you’ll be allowing advertising for your competitors.
And advertising for cars is commonly found on public transport.
Perhaps Metro is being big by not vetoing these slogans. But it does seem to undermine their own promotions.
Foxtel advertise regularly on commercial television, but I don’t remember them saying “this show is boring — the channels on Foxtel are much more interesting.”
(Tip thanks: P.)