It started by taking over regulation of pipelines in the 1910s. That seems like a logical step to me, but over time their purview has expanded to O&G plants and energy production. They aren’t responsible for public utilities, but a lot of the winterization plans were around upgrading pipelines that froze in the storm.

According to Wikipedia they haven’t dealt with rail since 2005, but it’s been a lot longer since the RRs were politically relevant to the office.