It's all being blown bigger than it is:
I think the replies are not satisfactory.
E.g. take the sentences "After all, what benefit does the owner of an orphan work actually get from their copyright? They can’t earn any money from it, as nobody can find them to pay them." and the two sentences in the following reply which say the same thing.
I know an Israeli professional photographer who makes money, among other things, from shooting nudes for the private use of whomever is being photographed. The photos are naturally not registered, and belong to the person photographed. One time his studio was broken into and all the equipment stolen, along with photos still on computer for processing.
Say the thieves removed the metadata in Israel (to make it harder to trace the photos to whomever they stole the photos from), and put the photos on the Internet. If a UK porn site wants to put the photos on it's pages, then (a) the photos would appear to be orphan until published & the owner finding out about it, (b) the owner doesn't care about money, but rather about privacy, and (c) sorting ownership via international process could be far from trivial.
The answer have a strong bias toward the creative process and making money, at the expense of owners' other rights, e.g. to object their work from being further copied. It's convenient for the UK government to make money first and maybe pay it later, it might not be so convenient for the copyright owner.