Part of this decline is MBA-driven.
Beancounters ruin every shop they run, whether it be Boeing, or any ones that I've worked at where Mr. Money Bags controls IT.
In shops that Mr. Moneybags (CFO) do not control IT I've noticed things are much better for IT.
As someone who works at the crossroads of finance and oil&gas, I've often said "these clowns don't know how to run an oil company, they know how to run a stock, and that's not the same thing." That behavior isn't limited to oil&gas. Even Musk has talked about MBAs "parachuting in" to management positions without the slightest clue what they're managing as a negative.
Unfortunately, running the stock is exactly what the shareholders are asking for, and is why they keep getting hired. The solution, of course, is no shareholders. Although the last major software developer taken private caused quite the uproar.