That's the way the nations founding fathers wanted it. They did not want people to be thrown in prison and forgotten without receiving a trial for an offense.
To protect an un-judged person from languishing in jail forever, as used to be common in many European countries prior to the colonization of what ultimately became the US. The founding fathers were...
There is no Amendment that guarantees a trial by a jury of one's peers. The 6th Amendment guarantees the right of trial by an impartial jury, but not of a jury composed of one's peers.