UK haven't moved from the right side of the score board, nor much higher than the bottom of it for many years, so low scoring for us was even before Brexit was a thing.
The song and performer this year was rubbish, but I do still think there's something political or otherwise that Europe dislikes about the UK. But as suggested in the thread, if we could get an outrageous, quirky or eccentric performer in the classic style of Eurovision, something that really grabs the viewers attention, we might actually score some points.
On the other hand, UK has always been and still is the pioneer of 'proper' pop music. Outside of Eurovision, all these countries buy records from UK and US artists. Who knows of many pop stars outside UK and US apart from Abba? In other words, we're better than Eurovision, and Eurovision is all these other countries have to show off their talent which is usually forgotten about not long after, much like x factor winners that no-one can remember either.