Why is Gingerbread the Go-To 3-D Dough / What Am I Missing?

Hi, thefrostitute, Congrats on making your first post. I look forward to many more to come!

Hi, first, welcome to the site. I hope you enjoy it. Second, to answer your question, I'm not sure what you mean by "fairly large scale", but I do not suggest using the recipe you are using for other than small-scale 3-D projects per the note at the top of that recipe, copied directly below.

I use a sturdier "construction gingerbread" with bread flour instead of all-purpose flour when making larger (more than 10-12-inch) projects, as the extra gluten in the bread flour makes it more structurally sound. (I prefer to work with my cutout gingerbread recipe for smaller projects, because IT IS more delicate - though not extraordinarily - and, thus, tastes better. I usually relegate my construction gingerbread just for show pieces, as the added bread flour will toughen the dough.) Any recipe can work for 3-D projects as long as there is enough flour in it to give it strength and to prevent a lot of spreading (and not too much leavening, especially for curved cookie shapes), but I also suggest you reinforce cookies by icing them with royal icing  (or at least the backs of them), as ALL cookies soften with exposure to any humidity and can wilt over time. The icing also helps to seal and reinforce the cookies. I have iced 3-D cookies (usually not more than 12 or so inches) on display in my house for years now with no drooping, though eventually the icing at the seams may dry out and these pieces may fall apart. I also box and bag projects not on display. Large boxes covered with garbage bags can keep out a lot of humidity and cover some very big cookie projects, and cakes even. Best of luck.

Also, be sure you aren't rolling big pieces too thin. I roll very thin for embossed and curved cookie pieces (about 1/8-inch) but would not recommend this same thickness for "large scale" pieces.

I did see that was noted but honestly just wasn't sure how to quantify "small" -- I knew mine wasn't but, for example I'd consider the gorgeous vases/urns you make to be big as well so figured what the heck I'll just go for it. 

Parts of this piece are 12"+ and it won't be consumed so I have no qualms about trying bread flour -- didn't realize gluten had that property, how interesting! Would the flour substitution be 1:1? 

I rolled tests at both 1/4" and 3/8". They'll be iced eventually, I just hadn't gotten that far but with that tip in mind may adjust the workflow a bit. And ah, a trash bag, so simple!