The police budget for the Assange case was about £3.5m per year. That is a lot of money which could be used in order to address other areas which the police is accused of turning a blind eye to.
If spending more resources for that reason conflicts with your ideals, then that's not a point I'm looking to argue here. My point is just that it doesn't take a conspiracy theory to explain why the UK was willing to spend this much money.
Consider for example all the money that the police spent looking for Madeline Mcann (https://www.independent.co.uk/news/uk/home-news/police-madel...). Was she any more important than any other missing child? Not really. Was there a geopolitical motive? Obviously not. But hey, she was in the news.