Tekken Tag 2 sold bad because T6's middling reception, so bad they came up with a F2P game and I thought for a moment the franchise was dead.
Next to this I think TTT2 is one of the worst Tekken games. I don't like it. It was far too much to remember, drawn out fights... I even rather played 6 or better yet 5 DR. I did love TTT1 though, but it was essentially T3 with tag mechanics.
Technicallly, Virtua Fighter 3 is more advanced than Tekken 3 despite releasing nearly a year earlier, but its art direction and sound design are just not up to par.
VF3 absolutely crushed Tekken 3 on technical levels. But the cab largely collected dust here, while everyone kept gathering around Tekken 3, especially when a new time released character popped up. Namco understood the market better. No one bat an eye at VF3 and I am sure it was much more expensive for the arcade owners than a T3 cab.
I love VF, I absolutely do. VF5 FS is one of the best 3D fighters of all time. VF4 Evo on PS2 was killer too. But I always played Tekken more, there was more to do, more to unlock and a more active community.