Earlier quoted context omitted.
So that's around 7 million phones per year. Assuming around £700/phone and 30% profit (very rough made up numbers), that should be £1.5B/year profit. If the judgement is for £3B to £5B as the article states, I can see why they might decide to exit the UK market. But that only makes sense if they don't then lose the patent cases in other juristictions, and end up having to pay similar royalties anyway.
I'm not sure that leaving the market will absolve Apple of paying the judgement, so staying in the UK market will help them recoup the cost. Leaving would be unlikely to improve their bottom line, so the judge was right - no evidence Apple will leave. This is just posturing, which won't go down well in front of a High Court judge.
The judgement holder could then attempt to go after Apple in other countries, but I think that would result in a court case about whether that’s possible or not.