Golfs 2005–2012 for sale on carsales = 3400 (includes 720 GTIs, of those 90 are 3drs, roughly 12% of GTI sales)
More broadly, if we take those numbers at face value 2.5% of all Golf sales are (or were) 3dr GTIs. They'd probably be a bit higher when you consider 3drs haven't been for sale for a while now.
Volkswagen sells 15,000-20,000 Golfs per year, which by these dodgy calculations, equals 375-500 3dr GTIs.
In contrast they sold around 400 Caddies, 200 Beetles and less than 100 Caravelles last year. All of which are stand alone models, that would, I think, require more effort to "inventory" than a 3dr GTI.
FWIW around 800 Passat CCs would have been sold last year.
I'm quite happy to accept VW's decision, but I'd just like a better answer than "we don't sell enough." Or at least I wish they'd explain their reasons better as to why not selling enough is a valid reason in contrast to other model lines that are also low volume that don't appear in jeopardy of being dropped from the local market.
As noted, many/most buyers of a 3dr model would be quite willing to order and wait the 3-4 months for it to be built.