It was a contributing factor, not a major one. Their products were not competitive with Nvidia after 3DFX completed the purchase of STB and started producing their own boards.
Not competitive how? The only card to consistently outperform the 5500 was the GeForce 2 GTS[1], which was a half generation ahead. 3DFX fans would also argue that T-Buffering and other unique technologies made the image quality better.
What killed 3DFX was a combination of no AIB boards to push the architecture past reference; their Sega deal falling through and the delay (and eventual cancellation) of the 6000 as a competitor to the GeForce 2 and Radeon 7000 series’ (later tests of engineering samples showed it outperformed both). The latter being a direct result of the two former problems.
