He just doesn't pass the eye test compared to all-around players like Granlund, Rantanen, Aho, etc. who are effective night in, night out.
Right now Laine is a mediocre at best 5on5 player who can barely make the 2nd line of his team on even strength, whose statistics are solely supported by the fact that he has a cannon of a shot to utilize on a highly effective Jets PP. Rantanen, Aho, Granlund, Barkov are the backbones for their respective teams, while Laine plays second fiddle to players such as Scheifele, Wheeler, even Connor and Roslovic at times.
His projection of course is higher than that, but at 19 years old he's not really a "great" player yet. Just one that can be utilized to great effect, like the Jets are doing, when he's protected. The other players mentioned do not need any "protection" by their team, because they've already matured into full-scale, all-around effective NHL players.
I reckon Finns generally respect solid work ethic, responsible defensive play, chemistry with teammates, over a superstar quality that, so far, far outshines other attributes of the game (which Laine does have). That's why steadier players are being rated over him, even though Laine's goal-scoring is likely to see him out-shining the rest eventually.
I don't think anyone cares about him not taking part in the world championship, neither did any of the other NHL players.