#4 Randy Orton is a safe and reliable worker
Whether you love him or hate him, Randy Orton is here to stay until 2024 at least (per his contract). There's a reason why he has such longevity - even more than The Miz: It's because of the safe and reliable work rate that they have.
While every Superstar has suffered injuries in the ring, Orton has a reputation of being a solid worker in the ring and although he may not have 5-star classics all the time, the style he's had has ensured that he has prevented suffering from many injuries in the recent years (with his last major injury spell being between late 2015 to the summer of 2016).
We must remember that Edge has returned but he's likely in a situation like Daniel Bryan - where he has to get a medical check-up and clearance every time he steps out of the ring. To ensure that he's safe, they need a reliable and safe wrestler and Randy Orton is the perfect dance partner for that.