Considering the program assigned a young DL to you while you have 3 DL in roster, assignment of young academy players seem pure random. However, if the not-very-clever program really think, probably it genuinely felt that you need a ST.

As different managers use different formations & strategies and need different types of players, it is very difficult to design an algorithm to figure out positions teams needed. If I am the programmer, on assigning academy players, probably I will consider counting number of players in 4 categories (goalkeeper, defender, midfielder, striker), or in all possible positions (GK,DL,DC,...,AMC,AML,ST). The first method is too rough. The second method may assign some players in positions, say AMC, that many teams have none but don't need.

I think the best solution to give more choices to us, or let us giving instructions to scouts earlier.