It sure sucks that device makers just have to wait and hope someone writes free firmware. If only they had some way to cause the firmware to be written, perhaps involving things like "money" or "employees" or "contracts with vendors".
The alternatives to this policy are allowing all blobs, in which case the RYF certification isn't actually verifying anything, or not allowing any blobs, in which case RYF cannot certify any devices made after 2009 (something the author also takes issue with). Making it expensive and risky for device makers to rely on blobs is the only middle ground that makes sense.
You seem to miss that these devices are often full of patented parts, so in most cases even if the manufacturer wanted to, they can’t provide sources. Also, modems are often legally mandated to have certain firmware (so that restricted frequencies are adhered to)
The alternatives to this policy are allowing all blobs, in which case the RYF certification isn't actually verifying anything, or not allowing any blobs, in which case RYF cannot certify any devices made after 2009 (something the author also takes issue with). Making it expensive and risky for device makers to rely on blobs is the only middle ground that makes sense.