In the 1970s, there was apparently something in the water supply, because TV executives thought that it would be a pretty good idea to take popular TV shows and redo them in an animated format.
If that was all there was to it, this would simply be a very strange thing to do, and sometimes, that's as far as it went: Star Trek the Animated Series was essentially just a continuation of the original series in animated format, and there it almost made sense - elaborate alien/monster designs cost a lot less in animation. But most of the time, the folks behind these abominations (correctly) realized that the source material wasn't really suitable to a Saturday Morning Cartoon. And yet this didn't stop them.
This particular variation was almost entirely exclusive to the 1970s.
An alternate formula was to reproduce the original show in a half-hour format, adding a small group of kids and their pet as sidekicks to the heroes. For some reason, this was neither as popular nor as successful as the first option. Filmation proposed this for Star Trek, but Gene Roddenberry balked instantly and the direct approach was used instead.
Another formula was to take the existing show, and append the words "IN SPACE!"