With this part, I believe it's because these factions had their roster squared away 9 months ago at the least, going back a year or two perhaps, so there's not much need for new players right at the start. While I can definitely get wanting a proper supervisory team with all the rules, handbooks for each unit, etc all written out far in advance so they're ready to just go for it at launch, it does suck that new players aren't able to chase those opportunities because the PD, for instance, already filled up a roster of 120-ish long before a launch date was even given.
That said though I saw a posting earlier today that FD was opening soon, so it's not like they'll all just be closed forever.