If it's aluminum, cost savings while doing the job would be the reason - most electrical distribution is aluminum conductors for that reason.

Depending on wire size Mac-Block or Polaris connectors are approaved methods of joining aluminum and copper wires. Use a torque driver and tighten the screws on the connector to the manufacturers specification for the specific connector and size of wire, neither too tight nor too loose.

If it's aluminum, cost savings while doing the job would be the reason - most electrical distribution is aluminum conductors for that reason.

Depending on wire size Mac-Block

Image source, example, not endorsement

or Polaris connectors

Image source, example, not endorsement

are approved methods of joining aluminum and copper wires. Use a torque driver and tighten the screws on the connector to the manufacturer's specification for the specific connector and size of wire, neither too tight nor too loose.