Story telling is increasing. You just can't tell. Acting is becoming superior as well. It doesn't make logical sense for everything about the movie industry to improve except for story telling. Think about this statistically. Most likely what's going on is warped perception.
I'm about 40 years old. For all 40 years of my life it's been the same problem. Why are all modern movies shit? In the 80s. Why are all modern movies shit? In the 90s... Same question... In the 2010s... Same chanted cliche mantra.. and now in the 2020s you're saying the same stuff they said was crap in the 80s is now good?
No it's a mirage. It's because all movie makers are in a constant race with audience expectations. New original plot patterns are novel at first, but eventually bore audiences and movie makers have to now improve. They copy a good pattern for a bit for some profit but audiences wise up and start saying what they say every decade. "Modern movies are samey and crap." But really it's getting better.
Take a story like inception. There's nothing like it if you rewind time 30 years back. Inception is a movie of the times a indicator of growing audience sophistication and movie making sophistication.
Even avengers end game is a sign of the times. If that movie and the whole franchise came out in the 60s at the same quality it is now it would have floored everyone and won academy awards across the board for story and effects. However because it came out recently there's a large cohort of people who call marvel stuff cliche and stupid. Why? Because it's not too divergent from the tons of movies that came out at the same time.
Take, everything everywhere all at once. That's another movie about directors forced to push the boundaries of story telling because of huge audience sophistication. Multiverse stuff is the latest trend but eventually that will get bland and you'll hear the same shit from hipsters about how crappy everything is.
Modern movies aren't all crap. It's because the pace of improvement is too slow so and because directors re-use popular story telling devices and plot patterns for about a decade that makes things seem shitty.