Ask Lemmy

Not inherently, but I think there are some factors that can make it feel that way, including:

• There was a higher bar to getting air time back in the day. Having decent quality recording equipment wasn't something a normal person could afford, so they had to rent studio time. There wasn't an internet to put stuff out there with, so you had to get your music heard by the right people, who then had to decide it was worth playing. Today is a lot easier to get something out there.
• Though every kind of media has been subject to crafted and pushed personas for decades (e.g., The Monkeys), in these days so much of what we're exposed to is what algorithms and corporations think we'll buy. Way more true today than ever before.
• As someone else mentioned, when people compare "today's music" to music from a prior decade, they're usually comparing everything on the air today to everything that's stood the test of time from the prior decade. Classic rock stations don't play everything, just the stuff people still like. There's a lot of junk that's been forgotten.
• This is anecdotal, but from what I've seen, people's musical tastes are based largely on what they liked in their late teens and twenties. Even if they like new music, it tends to be music that's influenced by that same earlier music. As with any generality, there are lots of exceptions. But I think a society's tastes evolve over time more than a person's tastes, so it's not unusual to get older and think everything new is crap.