I think that most of your major points can be said of any project. Every project requires a sponsor, a champion in a position of power from which you can gain legitimacy. Additionally, leadership, organization, management, and accountability are all vital parts of any project.

So what makes ERP projects more troublesome than other projects?

It has been my experience that ERP projects go off the rails for two reasons. First, I think that many organizations undertake ERP projects without any understanding, or worse, incorrect understanding of how their workflow and supply chain actually operates. The implementation happens at a technical and managerial level that is removed from the actual operational level to the extent that there are incorrect assumptions about how things actually get done. Then once the roll-out of the systems occurs, there is reluctance to use the new systems and extensive workarounds are created by the staff that uses the systems, negating the productivity gains that are hoped for.
Secondly, as Eli Goldratt has taught us, when new technology is added a systematic review of the business rules that were in place that enabled the old technology must be reviewed and changed before the productivity gains of the new technology can be realized. Too often, an ERP is put in place that could give you instant feedback of production, sales, inventory, etc., but reports are run once a month just like they were in the old system because 'that's the way we've always done it'. Your tech just got more agile, but your decision-making capacity is just as slow as it was before because of the rules that make up your process.

The multiplier in these difficulties is the visibility and costs involved with most ERP projects. There is added pressure for positive results when you have a project that is as costly and touches nearly every part of a company like an ERP project typically does.

Technical excellence is generally not the complaint in a failed ERP project: The data is usually good, the page-load times generally snappy, the interfaces almost always better than before. The complaint is that the system doesn't actually make the decision-making process within a company any better and it doesn't actually make them more money.