Bail Offences while committed on bail is considered as aggravating due to the fact that the individual has essentially reneged on a promise to the courts that if granted bail, they will not commit further offences, which is the core condition for the granting of bail.  More information on Bail Applications

In gaining some understanding as to the reason why offences committed while on bail is seen to be aggravating, can be seen in the judgment of Street CJ in R v Richards (1981) 2 NSWLR 464 (at 465):

“As the lists of persons awaiting trial on serious criminal charges continue to lengthen, there are at large within the community an increasing number of persons on bail. Many of those persons will in due course plead guilty to, or be found guilty of, the offences for which they are awaiting trial. The community must be protected as far as possible from further criminal activities by persons who take advantage of their liberty on bail to commit further crimes. The only means open to the criminal courts to seek to provide this protection is to pass severely deterrent sentences upon those who abuse their freedom on bail. This will ordinarily involve a significant accumulation of the sentence for any subsequent offences on top of the sentence proper to be passed for the original offence. It must be made abundantly plain that persons at large on bail cannot expect to commit further crimes “for free”. On the contrary, they will receive salutory penalties for the very reason that they have abused their freedom on bail by taking the opportunity to commit further crimes.”