[Swizec]

It makes sense when you think anout it. These missions last months even years before a specific piece of software becomes useful because it’s for a specifi part of the mission.

Wouldn’t you want the benefit of those extra months to perfect the software?

[marsRoverDev]

I think that in some cases it's simply due to the launch schedules being more optimistic than reality; the hardware has to be done, but the software development doesn't necessarily have to stop once you launch the thing.