I can only speak for myself personally because I don’t know how @dezbee2008 goes about it, but I keep a running playlist of possible contenders throughout the year. I’ll read music articles/reviews, listen through artist discovery playlists, and take suggestions from friends/family etc. In this case, a recent release won out.
To be honest, I don’t personally prioritize winning. It would be nice, and I do try to choose a song that I both like and that I think will do well (which I very much though this one would.), but ultimately I just to try to share wonderful, interesting music.
Also, on the topic of this particular entry, it wasn’t my first choice. However, it was most well liked amongst our jury and my friends and family.