[WillPS]

Worth noting all their linear channels other than ITV Be and CITV outrate ITVX, though +1 channels is a different argument.

Imagine ITV3 and ITV4 especially cost significantly less too - and remember providing ITVX isn't free to ITV either - there are still transmission costs and even a few thousand watching on a +1 maybe a cheaper way to reach that audience than if they streamed that content instead.

What "transmission costs" does ITVX have? I don't think they even have one of those placeholder broadcast channels (ala Pop Player) do they?

You probably mean bandwidth costs, which isn't at all the same thing and (unlike transmission costs) can be scaled according to demand (=revenue). ITV X also has an ability to capture revenue directly from the user, which of course broadcast does not.