An argument could be made that non-pub goers are still excluded from some kind of reward or compensation. If the buyer was spending their own personal money that might be one thing, but more often than not the funds come out of company expenses.

In consulting companies I've worked for (and I'm inclined at least in part to agree) it would be argued that it is not necessarily equivalent to compensation since work is usually talked about in some capacity at these events.

That's why they don't mind paying for these, because it is seen as additional collaboration/problem solving time. but they 100% would not be okay with handing out additional money to those who do not wish to attend.

Edit: To clarify as well, I don't think people should feel forced or inclined to attend these events for whatever reason they wish, this is just the argument I know and quite literally is in onboarding training I've taken.