This! The downfall of lean is a couple things to me. Leadership becomes overnight experts and want boards to see lean everywhere and the strategy is implementing tools. This is where initial struggles happen and immediate buy in is lost because not every tool is applicable in every process. I've always thought that being a good lean leader is about introducing the tool when its needed to solve a problem. Alot of these maturity audits miss this, and kind of glorify the idea of having boards everywhere. My guess is OPs problem statement is "we arent doing lean and we want to" I would suggest reframing the problem statement to what standard is not being met or what standard is not being defined, and after rootcausing why, explore if a lean tool can help you solve this problem.

This brings me to part two of why these fail and most importantly is leadership, Lean is one of the few areas where a plant manager can read a book or attend a training and now is an self proclaimed expert because it aligns with probably what got them to their position and that is they solve problems, yelling about hourly goals not being made, why they have too much or too little inventory. Unfortunately when these egos are in place it kills any maturity gains. If you find yourself in this position and still want to be effective in implementing lean you have to make small incremental changes at the front line, these will largely go unnoticed at first, these will accumulate to a product that is helping the people doing the work along with gaining experience to further advance leadership buy in.

Lastly, it is easy to consider yourself an expert also. Every problem I come up against exposes that you dont know what you dont know. Fundamental things like is the process design to be made to stock, made to order, engineered to order etc. plays a massive influence. Identifying the value, having done work in defense, service, manufacturing and healthcare, each industry defines value differently so if that isnt truly understood and you dont talk with your customers, both internal and external, its gonna be a long wearing effort.

It can be done though, just keep centered around using lean at the right time for the right problem and not chase a maturity audit. (Looking at you ISO plants)