Again the idea is to have a strong incentive to report for trial. Assuming your actually emotionally close to the person being offered as bond (ex: I wouldn’t let my brother go to prison) then you’d make sure to show up.
In the case of the person who has done no wrong and knows they will show up to trial, it reduces the cost of the bond to effectively zero. For the rich you’re able to put a price higher than just money, the actual freedom of someone they care about.
Note that this entire system is predicated on a judge deciding if the person being offered for bond being worthy of the position. Otherwise you could have rich people “buy” their freedom by paying off a sap to sign their name.