But eg just giving companies cash would also trivially increase their ability to pay higher salaries. But obviously, that's not really something anyone advocates for.

Right because cash comes from government which comes from taxes which come from companies' profit. Cash has value because governments put some limits on how much there is. Of course, they do end up printing some and dilute the value. They don't just hand it out willy nilly.

And even if there was a windfall, eg imagine something silly like a gold meteorite just falling down on the treasury building: there are always opportunity costs to consider.

But monopoly profits aren't too different: they don't just fall from the sky either. An enforced monopoly like those granted from a patent works by restricting what other people can do.