Isn't it unfair that rich criminals can pay bail and poor ones have to sit in jail awaiting trial?

Your question umes a fact that is not necessarily true- that "rich" criminals get out on bail but "poor" criminals stay in jail. In setting bail the judge will take into account many factors including: (1) the defendant's past record; (2) the seriousness of the crime and the strength of state's evidence; (3) the defendant's ties to the community; and, (4) the defendant's financial ability to post bail. In other words, a "rich" criminal who has a terrible record and no ties to the community may have his bail set at $100,000 for the same crime that a "poor"criminal with no prior record and substantial ties to the community would have set at $2,500.