Like most industries there is downtime over the Christmas period; that would be the same for dev teams and it would be a very bold move in any dev arena to push a release over that period. I'm also suspecting from what's been muted online that the Beta has been progressing well and with low impact issues identified so rather than the anticipated smaller 4+ builds that they are consolating it into an official full release at build 3 then a potential patch build to mop up anything that would push in conjunction with the monthly sec update