It seems like a bonkers practice to me. I understand that it is important to hire good people. But this could be delegated several levels down, at least for entry-level hires. I suppose the top dogs could worry about promotions and hirings starting at the level of the junior managers, if they wanted to.
Your position may have been opened before the layoff decision was made, so they decided to leave it open so as not to raise suspicions (managers will rightfully get upset if headcount is taken away from them with no explanation). They might've know the number of people they needed to cull in January, but not decided where it would happen.
There's a lot of work in Seattle. If you're cunning maybe you can get a second hiring bonus in Q1 2019.
And yet it is always the low-level folks who get fucked, while the executives who make the lay-off decisions often are rewarded with promotions and bonuses at the end of the year.