At one point there was talk of moving Roman Reigns from RAW to the SmackDown Live brand as part of the Superstar Shakeup.
The Wrestling Observer Newsletter reports the reason the move never happened is because if Reigns was moved to the blue brand, it would also require them to move Braun Strowman and WWE Universal Champion Brock Lesnar as well. Plans for the top storyline of the summer involve Strowman working against Reigns to get to Strowman vs. Lesnar while keeping Reigns vs. Lesnar alive with the idea of keeping them apart as long as possible.
WWE is still planning on doing Reigns vs. Lesnar at WrestleMania 34 in New Orleans.