Why such a delay getting Videophones on the market?

Answer 1

Because nobody wants to have to get dressed to answer the phone.

Answer 2

If you mean video phones as in camera phones that can shoot video, then they're already around.

If you mean video phones in the context of video conferencing, it's not clear that a lot of people really want them. The other thing is that pushing a video stream around incurs a lot more overhead than pushing around audio, meaning infrastructure upgrades in lots of places, which is an expensive prospect. There isn't a lot of incentive for the telecoms to support or market them.