Why does it take 2 years to stand trial for a petty crime? Why is the accused sent to prison while awaiting trial for a petty crime?
Edit: added 'in this particular case'
This actually almost happened to me, though not at Rikers island: I was arrested under a false accusation of a crime I didn't commit, and while I was supposed to have been released after an hour, there was some mess up where they thought I'd already been released and so kept me in there for around an extra 12 hours. It only even got fixed that fast because my lawyer made a huge deal out of it.
Now imagine the same thing happening, but without a good advocate on your side, in a much larger prison, and ongoing for years or decades instead of just half a day.