What could be the reason your ship date being pushed back?

Medical. Administration. Lack of Class Seat/Date. Any number of reasons. Have you spoken with your Recruiter as to why your Ship Date was pushed back?

Several reasons. It could be anything from medical hold, other administrative issues holding up the works, funding, transportation, there could be delays due to weather/natural disaster/safety concerns, lack of seats, and the list goes on. Talk to your recruiter.

The usual culprit is they're trying to fill slots to ensure a full training cycle. Typically there are four platoons in your BCT Company, full of recruits trying to become Soldiers. If they don't have enough bodies you'll get pushed back until they do.

Other reasons could be administrative or logistical, maybe they're short on staff or maybe they don't have the barracks ready.

Honestly it's a real crap shoot, could be any little reason.

Check with your Recruiter.