The Ferrari powered teams are not using 1st gear anywhere so it looks like they have a shorter 1st gear than the others, making it more difficult to enter that gear at speed, or locking the rear more (outside of launches). There are other possibilities. I am only speculating, but none of the 3 teams are using it.

I think it's because Ferrari have optimized the 1st gear around starts. There's a story that came out recently revealing that Ferrari is against changes to the start procedure that should help make starts easier and more predictable. So they have clearly made a design compromise to maximized starts and don't want to have the regs changed out from under them.
This is not to say one approach is better or worse, but only to say different teams have elected for different compromises. Another benefit of being a works teams with their own PU is the ability to choose these compromises with respect to the gearbox and the PU as Ferrari and RBR have each done.
