Over the past 20 years, I have met, professionally and personally, a number of people who have worked in senior roles at the club, during which time I've been told various bits of of info, gossip and chat. It's not usually your classic ITK and I wouldn't post anything specific if it was; it's generally just the kind of thing you'd hear from anyone talking about their workplace/boss. The difference being that in this case, the workplace is Spurs and the boss is DL. So obviously it's fascinating if you're a supporter.
The consistent theme I have heard is one echoed not only in public by Mourinho/Conte but also by others involved in both the playing and non-playing side of football at the highest level. There is a perception, which is arguably too common not to be given some credence, that Spurs under DL is/was not set up to succeed in the same way some of the other 'big clubs' are. To quote someone who's not an employee but has a very well informed view of top-level football, it looks like a super club but it doesn't act like one. There isn't a "culture of excellence" from top to bottom: it's skin deep. When Jose and Conte said it I thought it was sour grapes, and I was never sure exactly what they meant. But maybe they had a point.
It appears to me that's exactly the kind of insight the US consultants would have uncovered in their private interviews with club employees (and it's been hinted at in the public statement). Basically, DL, for all his strengths and achievements, has built a football club that's ideally placed to become a super power in the game, but he has no experience of actually running one. It's the single aspect of his job he couldn't master; he simply doesn't know what it takes to make that final step. He tried to address it by hiring Scott Munn and that didn't work; ultimately his bosses decided that the limitations and blind spots lie with him.
This may be about a sale, it may be about the Lewis family's frustrations with not winning, it may be a combination of the two. I think it's just the recognition that after 25 years taking the club almost to the summit, DL hasn't got what it takes to actually reach it.