Well for starters, this was the 70s - the space shuttle's development started in 1968 and its maiden flight was in 1981. The last spy satellite program to use film ran from 1971 to 1986. Further, the issue wasn't a lack of knowledge of TV signals - the first wireless video transmission had been made in 1923. The issue was producing digital video cameras of sufficient quality for the task in an appropriate size, and then transmitting such large files to the ground. Nobody in 1968 foresaw the massive improvements in digital electronics miniaturization that would unfold over the coming decades.

Rather than "very late to use tv" they were "very early to use CCDs". Even so that only happened in the 1980s. Before that film had to be used, same as we all had to use film for our holiday snaps until 2000.