#3 To make up for Finn Balor's RAW absence
Rollins has been obsessed with Ambrose over the past few weeks on RAW, as he should be because Ambrose has caused Rollins to act irrationally and lose his temper. This has happened on more than one occasion. And it's been building to a boiling point, obviously to spill over to a boil at TLC.
He's been kept away from the Corbin situation on RAW. And therefore, it was strange to see him come out to confront the General Manager Elect and put him on notice. It could have had to do with Finn Balor's absence on RAW.
Balor had been leading the resistance against the corruption of Corbin. He had to miss RAW this week because of injury or illness, based on which rumour you choose to believe in.
Hence, Rollins vs. Corbin!