I think it's a classic case of a company getting complacent because of a monopoly. Intel have basically become a marketing led company designed to make as much money as possible with incremental updates, rather than the engineering powerhouse from a couple of decades back. The lack of any serious competition has helped Intel's complacency. As you say, they've barely innovated, merely copied other people's inventions that have become industry standards.
That's fine if you've got great products being developed and ready to go behind the scenes, your competitors aren't executing, and you're still making a lot of cash. However, when someone like AMD pulls out a better product that's cheaper to make and sold for less, then you are stuffed. Intel has been hit by a perfect storm. AMD with a cheaper, better product, Intel design failures effectively making Intel chips slower or less secure (take your pick), Intel hitting process walls and unable to transition to 10/7 nm. Intel have been caught with their pants down because they didn't look to the future and plan for it, they just kept thinking that people would have to buy what they made because there were no other alternatives, and that just seems to be hubris that will catch you out, sooner or later.