SQL is an ISO standard. IBM would only have grounds if any part of Oracle's implementation implemented a proprietary portion of an IBM database implementation. This is the positive thing about standards, it removes ambiguity around what people can/should implement and present to users of the systems.
The IBM implementation of SQL far predates the ISO standard. Does something being standardized somehow relinquish the copyright? The idea of APIs being copyrightable is new, has IBM somehow relinquished its copyright claims for SQL to ISO? This article discusses the possibility at length https://arstechnica.com/tech-policy/2020/03/before-it-sued-g...
I think you have to have demonstrated that you have taken steps to protect your copyright. I’d imagine submitting to a standard would relinquish that. Patents on the other hand ...
You absolutely do not have to protect a copyright. Even if a book is out of print, you can't start selling it--or even giving copies away for free. However, although IANAL, I assume that submitting something to a standards body and having it accepted allows those standards to be used in accordance with the terms of the standards body--which BTW may not require that use be free in all cases.
Also note that even for established patents, a ton of standards standardized patented technology, and implementing the standard requires a patent license! This is a huge part of how Qualcomm makes its patent revenue from 3G/4G implementors.
