there are a number of reasons for this dearth of "composers" :
1. The media of choice used for composition today is the digital domain. The ccurrent samplers and sequencers are designed to provide a lot of "instant satisfaction" thru the use of loops , drum grooves and samples. Only students serious about learning the traditional basics through a college program or a mentor.
2. Those who ARE serious about composition for the most part dream of scoring films or producing pop records as opposed to composing for live jazz ensembles ( which is a crime considering the level of talent availble in many schools these days )
3. Learning this stuff is HARD -and most younger folks have very short attention spans -not to mention all the various media and cyber distractions:
Facebook, Twitter, Cable, iPods full of rotten music, etc .
you get the idea ....