Samsung wanted to prove that it is in no way behind TSMC when it comes to manufacturing process milestones. Even though TSMC is already rolling out a good chunk of 7 nm chips for various companies, it still does not use the EUV tech. Samsung will make full use of the EUV lithography by mid-2018, and then it plans to release 5 nm, 4 nm and 3 nm chips by 2022.
https://www.notebookcheck.net/Samsung-releases-roadmap-to-3-nm-fabrication-process.305254.0.html