Probably the biggest reason is money. Adding VIVO added to the manufacturing cost, and sales are lost to competitor cards that are cheaper because the buyer decided s/he didn't want to spend extra for VIVO.
A good example is HDCP: it has been supported as far back as the nVidia FX5700 and the Radeon 8500. However, not a single card sold for years afterward was capable of HDCP at 1920x1080 resolution because no manufacturer wanted to increase their costs, which included licensing the HDCP decoding keys from Digital Content Protection, which they would have to pass on to the consumer...and sales are lost to competitor cards that are cheaper because the buyer decided s/he didn't want to spend extra for HDCP.
I remember buying a Ti-200 Personal Cinema card that blew away my old Marvel G200 (and put AIW playback quality to shame). If I remember correctly, nVidia supported Personal Cinema thru the 6000 series...but while a few manufacturers released FX5200 versions, I think the last Personal Cinema card released was the eVGA FX5700. Once I needed to upgrade my Ti-200 for a Gallatin core box I was building, I realized I could have saved several hundred bucks if I had bought a separate PCI tuner at the very beginning...so I bought a Compro VideoMate Gold, and it's still in my box after several more video card upgrades. It's the oldest component in my current box.