I don't think Määttä is half as bad as Ristolainen. When he has declined, always seemed to have something a little more tangible than just "no motivation" or "I want to train".
One thing that might motivate Määttä is wanting to raise his olympic stock. The way I see it, right now we have two names who are 100% locks for the Olympic team: Heiskanen and Lindell. Then I'm putting Ristolainen and Hakanpää at 95% certainty. But beyond those four, there are at least six quite evenly matched candidates competing for those remaining four slots: Vatanen, Jokiharju, Nutivaara, Määttä, Lehtonen, Välimäki. And we don't know if some not-quite-there name like Heinola or Vaakanainen could be making quick inroads into serious consideration come next season. Juolevi also seems to be right on the cusp, finally.
But we know what Jalonen will do (well, what almost any coach will do) if he has settled on six already and is pondering with four to five names for the last two spots... he's going to pick people he already knows.