On the contrary the expectation of committing very substantial and expensive resources with no expectations of any end result does in fact stop the criminal process from operating in the same way that the expectation of refusal stops me from booking a flight to New York and asking Scarlett Johansson for a date. This is probably why people have been grossing each other out since the internet existed but no American has been so prosecuted for mere offense.
If you want a good preview of what trying to enforce UK law on US citizens looks like look no further than the New York Libel Terrorism Protection Act later passed federally as the "Speech Act" preventing US courts from enforcing British Libel judgements referring to you lot colloquially as "Libel Terrorists"
https://www.npr.org/sections/parallels/2015/03/21/394273902/...
Insofar as action purely in the UK well Europe is 10M sq miles the US 3.8M whereas the UK is a 94,000 sq mile island on the way to nothing else.
If they want to commit at minimum thousands of dollars in resources they can at great expense reduce by 1 the potential tourists spending money on their island I suppose.