Well that, and I'm sure they don't have a 'Central Park' asset lay around
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These things take time and money to build ykno! I'll gladly pay for year 2 DLC if it keeps the studio churning out fresh content. Rather that than abandoning a perfectly good base game and trying to flog me Division 2 for £60 in 2 years time. There's huge amounts of untapped potential in the game as it stands.
Yup no doubt it takes time to do that stuff but this is how the game industry rolls (and most industries for that matter), why give everything they possibly can in one game when they can withhold said ideas for DLC or even another game down the line, it makes no sense financially.
It will give people more incentive to buy the next game/DLC if the content is actually something people really want and central park most certainly is so I won't be surprised in the slightest if they don't release a central park setting with next years DLC as it will be a massive selling point for the sequel (where I imagine they will generate far more profit than if they were to sell it as a DLC pack).
However, with the player base dropping significantly not long after release and never really picking back up and holding those players (didn't look like many bought into the DLC stuff either), in some ways, releasing something as big as central park setting could get a lot more people back into the game than what UG and survival achieved and set massive/ubi up for doing well with the sequel. For all we know, they could even take the division 2 to a completely new area/setting...
Another perfect example as to how big ideas are withheld for DLC/sequels is star wars battlefront, we were told that space battles hadn't be removed for DLC purposes, fast forward to a few months ago and it got its very own DLC and now supposedly the next battlefront will contain considerably more depth.
Same goes for batman arkham knight, so many villains that tied into the main story line had been removed for DLC purposes.
And with BF 3, all the changes we wanted to see (which could have been easily done) were withheld for BF 4.
etc. etc.
Regarding DLC VS a sequel, I don't really mind, as long as the DLC has replay value, which lasts longer than 2 weeks.