To be fair: the quality of movies produced by Hollywood has gone rapidly downhill already in the 1990s. You only need to compare the movies Quentin Tarantino makes; now personally I think Pulp Fiction is still by far his best work, but I concede that the movies he created lateron were above average (though I would not go as far as many others, who'd rate these in the 8 to 10 point ranges; I'd go more between 6 to 7 or 7.5, largely because there are a few smaller issues cropping up and I always notice these when I compare them with Pulp Fiction, which was really good; actually really well-made).
I noticed this in the 1990s in many movies. For instance, Independence Day - the computer animation pissed me off. I found them bad. Even Terminator 2, where evidently many people say it was great, I was nowhere near as convinced; I found the first terminator better and more "logical" and more consistent, too. But things decayed quickly in the 1990s really. Even movies such as Avatar I find total garbage. And while I am not totally against superhero comic/marvel adaptations (I liked xmen and in particular Hugh Jackman as wolverine), these are always the same formula. Tons of CGI, big fights where nobody knows what is going on, very little thought elsewhere in that formula. There are exceptions, but by and large these things keep on happening. Individual directors manage to break out of the mold (Chris Nolan) but by and large movies really SUCK now compared to the "oldschool days". And while some of this may be due to me becoming more critical, the production quality just sunk. Take movies such as Megalopolis - this captures what is going wrong. It seems as if the whole movie industry has partially collapsed in the last +25 years and they don't really know what to do to change this. The same has happened to games, by the way. It is almost as if only one formula exists only now.
Investment-driven development. When it's no longer about creating something compelling, but about convincing the investors that banking the production means a fairly safe ROI, you stop getting creative works by auteurs and you start getting sequels, remakes, and low-stake, inoffensive, mediocre, forgettable, bland sludge. At the upper end, investors give directors checklists and guidelines to limit their authorial voice. That's why it doesn't matter who the directors of the MCU movies have been. They're just Disney-produced movies. A film student could have directed them and it wouldn't make a difference.
I think discovery via streaming services also contributes to bland sludge. Decisions are made based on a name, category, maybe an actor and a single "cover" art image.