Maybe bookmakers are guided by the mood of the fans (or rather, the money that they bet on various outcomes). Perhaps fans from rich countries generate a greater flow of money for these European teams (Ukraine is also an Europe but eastern), so bookmakers are forced to give such odds. It will be interesting to see who is right in the end.
Bookmakers are probably relying on the U17 result. Where Wales beat Ukraine 3-1. And then you should also take into account the fact that Wales has Gareth Bale in their team. But honestly, I see Ukraine as having a better chance of winning this match than Wales. Now, it won't be an easy game, it will certainly be a very unbeatable match until the last minute.