What Vercel really did was make Next.js work well in serverless environments, which involves a lot of custom infrastructure [0]. Cloudflare wanted that same behavior on CF Workers, but Vercel never open-sourced how they do it, and that is not really their responsibility.
Next.js is not locked to Vercel. The friction shows up when trying to run it in a serverless model without building the same kind of platform Vercel has.
