Kids may be less creative nowadays, compared to the past, but I doubt entertainment has had much of an effect. For example:
neko-chan wrote...
The decline was especially noticeable starting in 1990s (I believe this is when pop music became really popular).
Pop music didn't become popular in the 90s. It's been popular since the moment it came out, which was arguably the moment music as we know came into existence. But avoiding that potentially treacherous conversation, let's say that pop music started being popular in the 50s - which it did. It was popular in the 60s, the 70s, and the 80s, too. It was different from what is considered "pop music" nowadays, but there are a lot of similarities. For one thing, music and lyrics that aren't too crazy or intense or deep. Listen to "Daydream Believer" by The Monkees and tell me if it's more interesting or philosophical than Justin Beiber's latest song.
It's the same with most fields of entertainment. Movies from the 60s aren't more creative than movies from the 90s, games in the 80s weren't more complex than the stuff that came out last year, and literature didn't fall from grace in the 70s (some would argue that it happened before the 20th century even started).
It's not about what entertainment is popular; it's about how we think, and the current state of education plays a large role in that. If we think that a box can only have six sides, then we are limited and it is harder to move ahead in bold new ways; however, if we learn that a box can have seven, eight, or eleven sides, then we can think outside the box (pun intended) and see things that are unusual and stray from the norm.
Public education, with its focus on standardized tests, is telling kids that a box can only have six sides, because when you're talking a test, there has to be an answer. At least, if you want a test that's easy to grade. But when every school in the country is taking the same test, you can't have in-depth essay questions. It'd take forever to grade them, and you can't set a machine to sort through essay answers and decide if a student has the right idea or the wrong idea.