There are many reasons NFL teams have a specific philosophy on whether to receive the opening kickoff or to defer to the second half. Some coaches prefer to try to get a lead right away. Other coaches attempt to get the final position of the first half and the first possession of the second. Other coaches make their decision based on what would inhibit their opponent the most. And some coaches change it up from week to week.
For the 2018 Pittsburgh Steelers, it seems to be more of trend to defer to the second half.