"hired the vendor based on a cool demo & vendor size" It is common that companies don't chose the right people to assess vendors and review the suggested approach. Often the consultancy sends in sales teams to pitch to the boardroom with demos and "we're Big Company X and know what we're doing". However it seems that Hertz knew enough to ask for specific functionality that didn't get delivered.

"did not have a Hertz employee as Product Owner" Part of leading a project is making sure that your client, internal or external, is properly educated and involved in necessary decisions. Accenture shouldn't have accepted the PO role as it is a conflict of interest.

"tried to go big fast instead of taking an iterative approach" I don't recall reading if this was Hertz's decision, it could well have been Accenture's suggestion and in the early stages of this relationship Hertz would have trusted their "expert" recommendation.

"did not implement proper tests & validation" This would have been Accenture's responsibilty.

"spent $10M without building internal skills" It was $33M and you're right, although we don't know what skills they built internally. They might have been better off building a team internally but often companies prefer to hire "expert" as it's often easier from a cost centre and administrative view.

https://news.ycombinator.com/item?id=19749477

Specifically: "Your customers are idiots, that's why they hired "experts." They don't know how to judge expertise (otherwise they wouldn't be hiring you). They hire based on emotions, recommendations and epaulettes because that's the best they can do."

"They might have been better off building a team internally". For a business critical projects, building the team internally and using the right partner is the way to go imho... if budget allows, which they had plenty.