It's not a singing contest, which is why the singer can be from anywhere and have nothing to do with the country.
@Happyjoe Political voting has always mostly been a thing, and the UK always had a much lower chance of winning even though it wasnt impossible in the past. As this has slowly got worse across the last couple of decades, the market of people who would want to do it has shrunk dramatically.
For anyone with either a reputation and position in the music world, or who thinks they have a realistic chance of getting one and a position, it is something with a high chance of poor PR, low positioning, and being tarred as the "Eurovision loser" - which for someone who might have a chance at making it could be an issue.
So the realistic pool of talent, is those who have failed to get anywhere because they arent' really very good, or would fail and they know it, and this is a last ditch effort to get their name out and maybe see if something happens.
If we could get someone famous in, if they were big enough they probably would have a good chance based on that. But they just wouldnt want to take that risk. Same as anyone talented looking for a real career.