From what he said in the video it’s a few things.

Firstly, they keep being disappointed with the performance. They somehow have to market devices that barely improve performance and battery wise at all. One of his sources called the new generation a waste of sand and said the writing is on the wall, it’s time for 50/50 Intel/AMD.

Secondly, apparently Intel has been very bad with communication leaving OEMs in the dark. That means sometimes they get information very late in the design process hindering their ability to get work done in time and other times they have get delays over and over again. I think that was a big issue with their discrete graphics.

This last one wasn’t mentioned in the video but look at the recent desktop fiasco. Intel gave MB manufacturers a spec, which they adhered to, that now causes stability issues. Their solution, changing the spec and saying motherboards pushed the power envelope to far. Hell I’d be pissed too.

On top of that as you mentioned Intel CPUs keep having new vulnerabilities because it seems Intel can’t improve performance anymore without trickery that causes problems down the line. I mean some CPU generations have lost over 50% performance since release because of exploit mitigations.