Because pass-through is most simple and compatible solution to the problem, while PowerVR approach only creates more problems.

The Serpent Rider wrote on 2020-07-30, 11:52:

Because pass-through is most simple and compatible solution to the problem, while PowerVR approach only creates more problems.

I understand the easier concept of just composing two analog signal into one, but I don't remember many or any problems with the PowerVR above cards. Drivers installed always easily, 3D games ran every times. Maybe I was lucky every test I did but sure were more the times I had problems with the feature connector. Some cards did work only with a single specific brand video card.
Instead I always found the PowerVR solution to just work and the better the main vga was, the better the final quality was.

Check DOS compatibility matrix. Quite a lot of cards struggle to render good frame rate with PCX. It's also quite possible there were some problems with specific motherboard chipsets, which were not documented well, due to obscurity of PCX accelerators. And let's not forget about infamously horrible driver overhead.

Innovative approach, but at that time it would have worked good only in closed ecosystem like Apple or game consoles.

The Serpent Rider wrote on 2020-07-30, 12:38:

Check DOS compatibility matrix. Quite a lot of cards struggle to render good frame rate with PCX. It's also quite possible there were some problems with specific motherboard chipsets, which were not documented well, due to obscurity of PCX accelerators. And let's not forget about infamously horrible driver overhead.

Innovative approach, but at that time it would have worked good only in closed ecosystem like Apple or game consoles.

I understand. I never thought into the overhead of its driver, actually I found them to be mostly stable but it was difficult to say how good the card was accelerating cause the few games supported. But the idea of the digital signal to the main vga without loosing any details and actually benefit (for example) of the great vga DAC of the Matrox cards of those times, still sounds like a great idea and what I wish other cards should have done like the Hollywood+ MPEG2 decoder and similar ones.
I suppose is the one of the only solution ever make in this way. But the external analog cable was a nightmare itself on the other cards.. it depended on so many variables..