You were pregnant. The matrix had coded Optimus with hyper-fertility and an intense desire to sire sparklings. And as his lover, you were the easy choice.

Unfortunately your house, though spacious enough for a newborn, just wouldn't cut it anymore.

So while you were at work, the Autobots began transporting everything to a warehouse big enough to support everyone. With a little extra for the baby. You wouldn't have to lift a finger, Optimus made sure of it.