television was different then, movies were different then. the studio system was still in place and very powerful. movies and television were more about formulas to draw as big an audience as possible. movies and television were like "chef boyardee", food in a can, every can tasting the same; formula, canned food - formula canned television. they didn't want Buffy to grow up because that would mean the death of the formula, they would have had to go through all the trouble of trying to create a whole new formula, that may not have worked like "chef boyardee" Buffy.
thank God things have changed! hooray for cable, foreign movies, and independent movies!
unfortunately the music industry has gone in the other direction. music is now dominated by the record companies, dominated by producers and the bottom line. most popular music today is the equivalent of television and movies back in the 40s, 50s, and 60s. canned, precooked, formula music. there was a time when music was in the hands of musicians ans songwriters, people well versed and educated in music theory, musical composition, and who could play an acoustic instrument, and music companies and producers would go around clubs, musical venues, or word of mouth, searching for the next big hit or next big musician, or musical group. but today most of the music you hear is based on a formula, something that was precooked and put in a can for you to reheat.
personally i think it's rap and heavy metal that are to blame for what's happened to music. when the record companies and record producers found out just how little it takes to create a money making "song" they probably thought to themselves, who needs melody, who needs harmony, who needs orchestration, who needs arrangement? you only need a thumping beat and a rudimentary rythm, and you'll have a product that will make us a buck.