[matthewmacleod]

It appears that the success rate of people understanding and implementing these things is very close to 0%

I don't think this is the case. You're likely only hearing about the failures.

Here's a counterpoint – we implemented Scrum. It didn't cause any real issues, increased the speed with which we delivered features to customers, and increased the visibility of everything that was happening both within the development team and within the wider business.

Part of that was having a dedicated individual responsible for managing and implementing that process who made sure that it was actually achieving things we wanted to, rather than being a tick-box exercise, and who isn't afraid to make modifications such that the process better reflects the needs of the team.

In fact, I'd argue that the problem is completely the opposite to what you imply – it's not that people don't implement 'true' agile or 'true' scrum, but that they try to do so, rather than using these systems as a basis for building a development process that works for their team. No true agile team is slavishly adherent to rules that don't work.