Course they did, but that wasn't MTV's doing. Queen's Bohemian Rhapsody invented the music video as we know it, in 1975.
That was the groundbreaking event that changed everything. The video was as important as the single. Every act from that day on wanted to duplicate or surpass "that video". The Buggles "Video Killed the Radio Star", was a hit in 1979. It was used unchanged in MTV's launch transmission two years later.
Music programmes were increasingly built around videos and clips, rather than performances. You'd get mostly videos with perhaps just one or two acts miming along to their single, or playing in the studio. By 81 all significant releases came with a video. MTV was just a place to play them back to back. Videos were very well established and expected by then. Which is no doubt why MTV launched.
Video certainly changed style over the 80s, and every other decade, just as they had 1975-81, but what doesn't evolve over a decade? The 80s brought more emphasis on production and direction. By the mid and late 80s videos were being shot on film, ran longer with far bigger budgets. Acts were starting to be created for video first, and with MTV and other music programmes in mind.
As I understood it (obviously with some exceptions), music videos were an expense for the band/label that fell under the general purpose of promotional material (like posters, magazine ads, etc.)
Of course they were a chance to be creative and have fun as well, but that can be the case for any promo material. The thing with MTV was that it was such a low cost concept for a network. Instead of paying for programming like most TV, music videos were essentially free (if not sold to the network in a reversal of the typical TV transaction).
It was like a paid infomercial for bands and albums, except actually entertaining in its own right.
