Why can't the handling agents pay proper rates and pass these charges on as any other industry would ?
Because in the grand scheme of things, two aircraft diverting to Scotland doesn't matter - to the airlines its a drop in the ocean, they won't pay extra for 99.99% of their flights so the 00.01% can get diverted to the most convenient place, it won't make the 24 hour news cycle, there won't be questions in parliament, there won't be a Twitter storm. just a few raised eyebrows on specialist forums.
And that's just like any other industry.