Whenever people see old systems still in production (say things that are over 30 years old) the assumption is that management refused to fund the replacement. But if you look at replacement projects so many of them are such dismal failures that's management's reluctance to engage in fixing stuff is understandable.
From the outside, decline always looks like a choice, because the exact form the decline takes was chosen. The issue is that all the choices are bad.
Even more glaring is TV shows, where you now get an 8-episode 'season' every 2-3 years rather than the old days of 20+ episode seasons every year, often non-stop for 5 or more years.
It's not so much about capability/competence as pushing production values to unsustainable levels. You could get away with much less expensive VFX, sets, and costume when filming in standard definition. Now every pixel is expected to look flawless at 4K.
Another more controversial factor is that everyone brings their politics/activism to work and injects them into everything that they do. Now everything has to be pushing for social change, nothing can just be entertainment for the sake of entertainment.
I like to use Star Trek in the 90s as a good example of what I mean. While there are episodes where the writers got preachy (they're only human I suppose), most of the time the writers were very careful to not openly take sides on the issues they raised. Even if you got the sense that the writer for an episode might feel a certain way about the topic, the characters wouldn't tell the audience how to feel. They didn't call other characters who disagreed with them names. They didn't just bully their way to victory in the story. The topics were treated as complicated issues where reasonable adults could disagree.
Compare that to shows/movies/books today. The writers treat the story primarily as a vehicle to express their opinions on issues. They have characters tell people "this is how a decent person behaves", with the understanding that the message is really meant for the audience. They have characters who agree with them call their opponents bigots or worse insults. They portray said opponents as villains or morons who only hold their beliefs because of how evil/stupid they are. They have the "good guys" run roughshod over anyone who disagrees with them, and they get to win despite their bad behavior. And often, the writers (and even other people involved like actors) will openly express their contempt for their audience when speaking about the work. They pick fights where none needed to happen, saying stuff like "if you don't like this then I don't want you as an audience member anyway". They are, in short, bad writers who don't have the skill to successfully let their social views influence their work.
The result of all this is that these writers don't succeed at persuading anyone. In years past writers could actually make progress on advancing the things they believed in because they had the wisdom to not openly preach to people and call them names. They respected people enough to let them draw their own conclusions, and as a result were successful. But writers today aren't good enough to persuade people to continue breathing, let alone something more controversial than that.
There is also an uptick in how much politics get forced into art, with people trying to claim "everything is political" and the like. But that isn't nearly as big a factor as how bad today's artists are at using political themes in their work.