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.
This system only works under assumption that the accused is honorable, but it's silly to think that people accused of crimes are generally honorable.
You'd end up with a lot of cases of a woman trying to help a deadbeat boyfriend who doesn't care about her or anyone else. Are you really going to put her in jail? Maybe he just leaves the country, and then what?
They are not comparable at all, and locking up an innocent person is unimaginably worse.
With money, this is much harder, because it's difficult to determine where money really came from.
Why do you think involving innocents is a good idea? Especially when it means they go to jail and get their freedoms taken away? People who skip bail already put their family at risk plenty of times, often signing away property and leaving family members destitute.
It would be much better to refund bail costs for anyone acquitted than to force this on people who do not deserve it.