It's not really hard to understand.
Youngsters under 18 can only sign 3 years contract so when we sign someone like Adnan he will be on a 3 year contract. Unless he makes the step up to first team within first year(which is highly unlikely for any player we sign at that age range) there is not much reason to offer them a newer contract. However end of the 2nd year is when we usually start offering newer terms but youngsters specially not the home grown ones will obviously prefer to stretch it out as far as possible because then they will have a stronger BATNA.
Januzaj's first season was troubled by that injury so it would have made no sense to offer him a renewal after that season. You can't blame the management much for the current situation, it is something that we should get used to specially when signing foreign talents of that age.
Didnt know that. Obviously the whole things makes a lot more sense then.