Kubalik was at development camps and even training camps when he was playing in OHL iirc. It was only last year he moved back to Europe that he didn't attend.
I don't fully understand why the Kings would want to move on from guys like Kubalik and Porkhorkin. The Kings aren't exactly overflowing with prospects or contracts, why not bring in these guys who have done so well in Europe for a chance. Kubalik really seems to be coming into his own, wouldn't surprise me to see him get an NHL deal in 2/3 years if the Kings move on. While it's still likely he will not be an NHL player, it's worth a chance on a late bloomer like Kubalik.
Kubalik in particular has already shown he wants to come to North America by coming over to play in the OHL. It seems it's the Kings who are not interested which makes zero sense to a team with a shallow prospect pool. Leading the Czech Extraliga as a 21/22 year old is pretty damn impressive.
This is complete speculation on my part, but my opinion is the Kings brass probably question his character or determination.
When he was in the OHL, and playing in Sudbury, he struggled. He was traded to Kitchener and struggled even more. Instead of staying in North America and continuing to struggle, or grow and adapt, he went to the Czech Republic.
I don't think the Kings were impressed that his response to adversity was leaving. I don't think it makes him a bad player or person, but when you listen to Lombardi talk about players who don't pout or sulk, and stick with it, I think we can surmise how he felt about a player going back.