It was wired this way because Goober the appliance installer guy, whose job is pushing heavy appliances around on dollies, needed to hook this up and collect the customer's cheque ASAP. Goober had a 3-wire appliance to attach, and saw 3 wires in the wall, and boom zoom and out the door.
You actually have 4-wire service to this range. However it is in aluminum wire, which is a serious problem. If the ground is aluminum, surely so are the hots and neutral. None of those splice connectors are rated for aluminum wire.
You will need to obtain some "MAC Block" connectors, which are a somewhat miniaturized version of Polaris lug connectors, which are proven to work well with aluminum.
- The two hot wires use a MAC Block to go from that aluminum wire to the corresponding copper wire from the range.
- The aluminum neutral wire is simply capped off; one of those wire nuts is fine for that, but tape it on.
- The aluminum ground wire goes to one side of the MAC Block. To the other side go 3 wires (which is allowed): the range's ground wire; a new jumper wire to the steel box; and a new jumper wire to a new hole in the cover plate. All need to be grounded.
... By the way, fix that schizoid lid.
On one hand, you've got a 4x4 junction box with a 2-gang mud ring that has 6-32 mounting screws in the correct positions to mount 120V outlets and switches. On the other hand, you've got a common 4x4 junction box lid that expects to attach to the corners of the box.
I see now that the junction box is blocked in by cabinetry. That isn't allowed and is a serious code violation: not only is it uncovered, but flammable materials are inside the box! Get a vibrating tool and cut away enough of the cabinetry above it that it's possible to mount a normal junction box cover plate the normal way. It looks like what's above that is nothing special, just the back of a drawer box or something, so it won't do any harm to remove the offending material.
Now you need a different lid that attaches to the 2-gang screw locations... a real electrical supply can help you out there. Home Depot won't have it, it's not popular...