From Wikipedia:

"Meta" had been registered as a trademark in the United States in 2018 (after an initial filing in 2015) for marketing, advertising, and computer services, by a Canadian company that provided big data analysis of scientific literature. This company was acquired in 2017 by the Chan Zuckerberg Initiative (CZI), a foundation established by Zuckerberg and his wife Priscilla Chan, and became one of their projects. Following the rebranding announcement, CZI announced that it had already decided to deprioritize the earlier Meta project, that it would be transferring its rights to the name to Meta Platforms, and that the project would end in 2022.

So, they bought it through their (non-profit?) foundation and killed it to harvest the name?