Why we build in Next.js and not WordPress
WordPress assembles the page on the server every time somebody visits. Next.js builds the pages once, when the site is published, and then serves them already finished. The visitor does not wait for anything to be constructed. That single difference explains almost everything else: the speed, the security and the maintenance cost.
A well-tuned WordPress can be fast. The problem is that it rarely stays fast, because every new plugin, theme update and third-party script adds weight. With Next.js the fast starting point is structural, not something that depends on whoever maintains the site being disciplined.