Young players don't really have a 'value' as such as they're more 'unknown' - this was to stop it making it easy to just look at newly generated players, see which were immediately highly valued then pounce as they'd clearly have a high PA. Now nearly all young players have this 'unknown' value and the only way you could find the proper 'value' is by offering for them. Once they gain a proper reputation with first team football and age then their actual value will reflect what the club feels they are worth. Hope that makes a bit more sense as to why it's how it is.