Why would a journal force me to register on ORCID?
Not only publishers start to collect/request/demand ORCIDs more and more but also institutions.

What is it all about?

It's about bibliometrics and author profiles. Being able to identify an author and its publications is useful for the institution and its authors. Authors benfit by having an accurate and complete publication list, even if they change the institution. Authors and institutions benefit because bibliometrics become more accurate, e.g. the author's h-index or the list of publications affiliated to authors of an institution.

Why are publishers taking action?


  We hope that our action inspires the community, including researchers, research funders, and research institutions, to join us in adopting ORCID and making it easy for researchers to connect their iD to their contributions and affiliations. source


Publishers want to enhance their services for authors by including ORCIDs in the publishing workflow.

Why are publishers making ORCIDs a requirement?

One reason I can think of is that they want ORCIDs because bibliometrics, especially impact factors, are important for them and the enterprise(s) providing the impact factor(s) are also interested in author specific factors like the h-index. Additionally, I assume, publishers also want to know and present who publishes in their journals. Think about a publisher stating that a nobel prize winner published most in their journals. 

Overall, ORCIDs solve a lot of the problems regarding author identification, which benefits authors (named Smith or Wang or ...) and institutions. ORCID itself is a nonprofit organisation. So far, I haven't thought so much about the benefits for the publishers to make ORCIDs a requirement. Maybe there are different/more reasons.