Comment by arghwhat
The threat of imprisonment if you don't pay the fine is the polar opposite of anything "symbolic". It puts individuals at significant personal risk should they ever make the mistake of traveling through the UK, in turn limiting their freedom of movement permanently even without being in prison.
This is just not that big a deal for people who don't have family or business connections there already. It'll be like 'oh no, banned from a once-great place.' Had the UK remained in the EU, they might have been able to get other countries to honor such an arrest warrant, but as it is they just look petulant.