Actually they did. In the last years of commercial film, the technology would allow you to shoot film and video (not digital) at the same time. The video was not quality, not high-res, but it gave you the ability to immediately look at a rough of what you had just shot. And that ability is a very powerful tool.
Tim
Yes, that's true, Tim, you're right. You could have a video split but no-one could really tell much from a 4" monitor off a Clamshell (though at that stage I wasn't working with TVCs, only music vids). Now there's a video village on every TVC for the client/agency with a couple of Panasonic BT monitors sat in front of a bunch of fold-out chairs (or sofas, for that matter). And M&M's, of course, but not the green ones.
It's certainly a powerful tool, but like all powerful things, can be abused if in the wrong hands.
Incidentally, the first things I ever shot were on 16mm (with no video split), but there were only two labs able to process it at the time. Less than a year later I shot my first music vid on the RED, but there was only one post facility that knew what to do with the footage (no-one had REDCODE so it was rendered out to a bunch of lossy QT files. It looked rubbish.)