There's also the simple fact that TacPack is a consumer entertainment, product (insert blah de licensing blah de blah here) and Prepar3D v2 contains much of the same functionality itself, through the "Professional Plus" packages.
http://www.prepar3d.com/product-overview/prepar3d-license-comparison/
L-M are aiming P3D at a professional military market and therefore have developed their own tools to work within it. Yes, $1000 per license is half the cost of a P3D Pro Plus license, but the simple fact that the core package contains content developed by a real-world military hardware manufacturer, versus a package developed by a consumer entertainment programming team, will hold a lot of weight with the target audience.
Ian P.
It's true Ian, that does hold a lot of weight. It's a David and Goliath thing to begin with, but nothing short of education can combat ignorance. LM sells military hardware, LM is huge, and LM has unlimited resources. However LM does not put those unlimited resources into P3D, much less focus them on the "combat" systems. Most of the people working on P3D were formerly working on FSX projects (and I'm not even talking about former ACES team members), with no background in military hardware applications, or even military aircraft simulations. Fortunately for us, many potential commercial customers do some basic research before they commit to the wrong solution. It took LM 3 (4?) years to put any emphasis at all on the one aspect (ya know, guns n' stuff) of the platform that even makes sense as a LM product, and they still managed to screw it up in so many ways.
First a little background for the uninitiated: There are no actual functioning weapon systems in the Pro+ package. There are placeholders, or Lego blocks if you will, for data which a developer can populate with "real" data, assuming they even have assess to it, but it is most certainly not provided by LM in any form remotely resembling realistic, and never will be for obvious reasons. The Pro+ SDK provides a container that has not been filled, and it's up to you to fill it using your own research, programmers and paychecks. Talented people with lots of resources and/or time could end up with some impressive accomplishments using those little Lego blocks LM provides, but it would take a whole lot more time and money than a comparable TacPack solution, and they'd have to write their own high-level integration systems all by their lonesome, because LM didn't do any of that either. Add to that the fact that Pro+ cannot simulate EO-guidance, laser guidance, or anti-radiation in its current state, and you've got the makings of a fine boat anchor.
And if these potential customers did a little more research, they'd quickly discover that oh, BTW, it doesn't work in multiplayer either! It's not a bug, it's a complete omission! LM must have made a boo boo when they forgot to advertise that fact on the Pro+ product sheet, but you'll note that they don't actually say anywhere in the specs that it IS multi-player compatible. Oh well, what's a little lie of omission here and there; It's only a $2500 product that can't be used to shoot anyone. I supposed they'd tell you if you asked, assuming somebody in their forums would actually answer the question, which is debatable based on the umber of hanging threads. It is therefore a very expensive single-player "solution" which is currently good for nothing more then sending even more commercial business our way.
BTW, the TacPack is not "$1000, not even close. Let's just say it starts significantly higher than that, and scales with the number of seats. However in the long run, it's a whole lot cheaper than paying a programmer or two to try to mold P3D into something that resembles a viable [single-player] combat system solution. Pro+'s $2500 initial outlay is only the tip of iceberg in long-term development costs. Couple that with lack of comparable functionality, and perhaps you'll understand why we continue to acquire commercial customers that either had no intention of going that route, or have already abandoned ship when they approach us.
We could not defeat the giant if it was awake, however it's clearly got a hangover and I couldn't be happier.