I remember being very impressed with Linington in a few matches around 2010/11. I really thought he would go on to become a PL referee at that time, but never quite happened for whatever reason. I think he might have had some injury issues? It seems unlikely it will quite happen now.
Robinson seems to have been in contention a few times and had a PL trial match in 2019. Has his chance passed now? I'm not sure we can definitely say that but I'm certainly a bit surprised he hasn't been appointed by now so perhaps it won't happen.
I guess being in the right place at the right time is also a factor. That's perhaps especially true last season where 4 refs were promoted in one summer to SG1, which I think is a record. You could have been the 4th best referee last year and got promoted and in other years been the 2nd best and not got promoted. We've had 5 referees promoted and 4 retire from SG1 over last 2 seasons, so I'm not sure we'll see those numbers repeated again for a while.