The article author is clearly assuming that, but I'm not sure whether it's even true to any meaningful extent. How many contributors to free/open content resources are even bothered that their work might end up being used for AI training?
Also, maybe AI firms should pay for the scanning and OCR text-extraction of existing paper-backed resources. There's a lot of, e.g. old academic research that's still not meaningfully available online, much of it is even free of copyright worldwide. If you care about ensuring that your AI's are adequately well-read, this is a bottleneck that might be especially easy to address.