The RIAA (and the wider copyright industry) were careful to never bring a case that might rule on the issue of "ripping data from CDs and converting to digital".

What they did was bring a case against Naspter, which ruled that ripping data off CDs AND THEN sharing it to millions of people over the internet was infringement. Not because of the ripping, but because of the sharing. The RIAA then somehow managed to twist public discourse to interpet the ruling as "ripping CDs is illegal".

They were careful, because the Sony Betamax case had already ruled that recording TV of the airwaves was legal, which is already a weaker case than ripping CDs you own. They knew such a case would likely rule against them, and they found the ambiguity to be much more useful.

And later cases like the google books case, and this Anthropic one provide even more evidence that the courts would likely rule that ripping CDs was legal if such a case was ever bought. (Though, it really depends on what you do with the digital copy)