Its because the newer breed of Alfas (156/147/GT) pips the GTV in so many areas, for example both ride quality & handling, driving position, build quality, convenience etc.
I don't agree. Neither the 147 nor the 156 ride well due to stiff, over damped suspension and flexible body shells, setting up a shudder that even my Spider doesn't have (and the GTV is a lot more rigid). The driving position in the newer cars is too high, which makes the body roll feel worse. Also you don't get the quality of materials in a 147/156/GT that you do in a GTV - real leather for the seats, for example, and anti roll bar bushes (another singular example) are always a problem on 156/147 and rarely a problem on the GTV. The 156/147/GT were made in the south of Italy rather than the north - there aren't many parts in common. In England they seem to have rust problems too. Then there are the electrical problems... especially on the CAN-equipped 147.
Convenience is also a moot point I think. Climate control might be dual-zone in the 147/156/GT but the heating and cooling is weak. There is no integrated Bluetooth or reversing sensors/camera etc. (convenience features you expect these days), though I do miss the rain sensing wipers of my 156. It's probably the only thing I miss, though.
The GTV/Spider were a more expensive car than the 147/156/GT and generally it shows, though you have to find one in good condition.
I find the TS uses half the fuel of the V6 yet gives 2/3rds of the performance, since it makes use of newer technology (variable valve timing, variable inlet, lighter components). I find it strange that V6s in the 166 break frequently and often aren't repaired, yet people here say that V6s are reliable. The TS seems more trouble-free to me - for example, no water pump problems, no cracked manifolds, less chance of the timing belt skipping. I had a TS with over 260,000km on the clock.