This comes down to AA trying to save money by having more flights in banks. Consequently, you're stuck with either a very tight connection or waiting for a long time for a subsequent bank of flights to connect. Whether this makes sense from a customer standpoint really doesn't matter to AA management. Inexperienced traveler usually don't have an appreciation for just how quickly a 35-40 minute connection can go wrong and they will be the last to get re-accommodated.