Why would it not be returned after he has shown for his appearances?
The bail bond company takes a high fee for putting up the money. The fee is the interest and risk premium the bond company charges. While Zimmerman gives the bail bondsman $100,000 the bondsman hands over to the court the entire $1 million. If Zimmerman skips bail, the court keeps the $1 million and the bail bondsman loses the million he put up for Zimmerman. If Zimmerman skips bond and is recaptured the court does not pay back the forfeited bond so the bondsman must collect from Zimmerman who likely will never have the means to repay.
The bondsman wins if Zimmerman doesn’t skip bail and goes to trial. When the trial is over the court gives the bondsman back the $1 million. He keeps the money Zimmerman paid up front as his fee. Given the risk 10% doesn’t seem unreasonable for the loan.
Ive never used or known someone to use a bondsman. I assumed there was a fee but I didn't expect it was 10%. That's pretty insane.