Why is Going Rogue Being Doled Out Piecemeal?

And so really, bringing up I17, did mean a delay to GR, but only a teeny one, and even then that's probably got more to do with something(s) they added.

I think most companies would be pretty happy with a product that was a little bit late if said product ended up delivering on more than they originally intended.

OP does your real name happen to rhyme with Mack Gemmert?

Rubberlad, I understand that you might be upset for ordering something with the expectation that it would arrive at a certain time and then having that time pushed back.

But I think you know well enough that computer game releases in particular are frequently pushed back due to technical issues. It's not unheard of for games to be delayed for all sorts of reasons.

So while I understand that you are upset, I also understand that the developers want to deliver a solid, working product with lots of content. The fact that you can play with dual pistols, and soon with demon summoning, is a perk!

Also, the focus of GR has always been Praetoria and side switching - ultra mode was just an added bonus.

When CoH and CoV was released, the endgame was added later, sure. But when GR comes out, we aren't leveling to 40 while we wait. Most people have 50s already, so unless that first incarnate level will take months to achieve, then there is a difference.

Okay, directly to your question: "Why is Going Rogue Being Doled Out Piecemeal?"

(We can only guess, but this is my honest theory... And I say this in all seriousness and zero snark)

Reality.
Things take time to get done, different things get accomplished in different amounts of time.
Honestly, they could have left out the Incarnate system as part of the regular/free expansions to the game (In my, largely uninformed, opinion), but their plans are to include the first part of it with Going Rogue and we will have to wait for the rest of it.
As others have said, the initial game was released with slated content to be filled in later and so was the other large expansion, CoV.
Perhaps this is somewhat of a standard procedure that displays a comittment to the paid-for-expansion... it is not simply something they kicked out to you that you have to pay extra for... It is something that will bring even more to you for your extra money that they will be working on after you've bought it.

The Pre-Purchase really is a nice marketing move.
As much as we like to point out the lack of marketing we see and how much we hate the limitations the marketing team puts on information, other players seeing Dual Pistols and (eventually) Demon Summoning will spur them on to being interested in those things as well.
Not everyone that plays knows all about what we know on the forums.
In-game advertising for the Going Rogue expansion is a nice move.
And, indeed, they are interested in the cash flow influx (As we've already seen with the Super-Boosters).

Whether or not they are running a good (great or terrible) business model... I really cannot tell.

The team at Paragon Studios, however, has my respect, admiration and trust just entirely based on what I enjoy in the game and what I see from them as artists, as people and as a team.

I don't see the way Going Rogue is being delivered as a problem, myself, but I can understand why you're wondering what the reasons are (Even if it is not something I considered).

If it helps, you might view it as a multi-course meal.
Pre-Purchase: two waves of large appetizers

I 17: The management would like you to have this complimentary bottle of wine and this house special soup and bread

Release: A sizeable meal that they hope pleases you greatly

Further additions to the "Incarnate" System: This could either be Dessert or a voucher for a free lunch