Possibly because for the extra cost of a GT, you could upgrade to a TB10 non-GB and most considered that worth it?
@Peter, I have seen one TB-series aircraft of any description within the last year and it was an early Trinidad. 25 years ago you saw more in the US, although never a lot, and I have no idea what happened to them. I suppose they’re mostly sitting in hangars unflown.
One is for sale and the seller claims the above.
It seems entirely plausible; Socata hugely overpriced the TB9 and TB10 in later years so the sales of the GT versions were negligible everywhere.
