It is his decision not to participate because he prefers to continue his development at the professional level. It must be acknowledged that Austria is participating in the Division 1 tournament, which is less enticing with opponents like Japan, Kazakhstan, Hungary, and France.
So, no, Reinbacher was not overlooked by Austria; he probably would have been their number 1 defenseman.
In fact, it's not even a surprise, as the Montreal Canadiens' first pick in 2023 had hinted at this decision in an interview with the same Marco D'Amico at the beginning of the season.