Holy Crap!!! I knew the label was spending a fortune on promoting Chicago, but that first video above used at least 4 cameras to film them recording. That was back when filming was actually on expensive film! And, it was at least a decade before MTV made videos a promotional tool to the consumer. That shows a massive investment from the label!
For all of you who hate big labels, they did (and still do) a ton of good stuff to get the best artists to market and provide their fans with content we want. Hell, that Chicago studio video alone is invaluable to true fans and it probably wasn't ever seen by the public until decades after the label spent a small fortune on it.
IN those days they made films like that to promote bands inside the industry. They were shown at conferences and trade shows to build excitement among promoters (for live gigs), radio stations, and even TV and Film studios for broadcast and movie productions.