One coauthor on a team can hijack the entire project by changing his or her mind late in the project and choosing not to publish.

When this happens, the withdrawn team member should sign a release of copyright to the remaining team members transferring all claims on the project to the remaining team members. The withdrawn member should allow the others to publish the research without his or her name. Otherwise, the person refusing to publish can gain tremendous power and punish the entire team by not agreeing to publish. This raises tremendous ethical problems for all parties. Without a copyright consent or transfer of copyright, the team has no choice but to attribute credit to everyone who contributed to the project. 

I find it hard to believe that a person would not know the intent of a team to publish the results of a research project if the original goal of the project was to publish the results in the first place. Not attributing credit to everyone who contributed would then constitute plagiarism. I also find it hard to believe that a person would contribute significantly to the design and data collection of someone else's work without an explicit or implied agreement to be coauthors. Perhaps a dissertation adviser, who is paid, would do it as a part of their duties and responsibilities. 

Moreover, an acknowledgement is what most people do in cases where a person contributed to a research project but did not agree to be an author.