devtrackers.gg
As far as I know Nelson is mostly working on II right now. He just updates Unturned 3.0 to make new possibilities for modders to let all modifications kinda lead the way of Unturned 3.0, while Nelson is working on II.
Just to bounce off this comment -- you basically answered your question of "what takes that long" yourself. The last couple weeks were used to provide necessary updates to U3 (alongside some other stuff that has been planned/requested but backlogged for a while).