Because those people aren't currently needed for the things that need to be done in sq42. They didn't move everyone, it seems like a lot of the people they've spoken about moving over are art related and some tech people that aren't needed for "polishing."

Star citizen hit a point where they knew that large complicated tech was going to take time to implement and they couldn't progress with content as the servers can't handle it until the aforementioned tech is in so I think they made a reasonable decision to pull as many people over to SQ42 while the networking people and the core tech people worked on star citizen. Within the next few months we're going to see if they can complete that core tech needed for the servers and that will allow for work to continue on as far as content/future systems.

All that said, Chris is absolutely horrendous at giving dates and I'm glad he stopped himself at citizencon this year. I would love to ask him what made him think 2020 was a reasonable estimate for anything lol