Congress writes laws with the assumption that ambiguities and complications will be intelligently and justly resolved by a human being - namely, these 9 people. The issue is not that one side or the other may fail to educate the Court, it's that the problems of "what the law says" and "what justice is" and "how the internet should work" may not be entirely coherent, especially when societal norms are changing as fast as they are today.
When the Constitution was written, the word "publisher" had a completely different meaning, completely unaware of the possibility of YouTube. Even in 1996, algorithmic Internet moderation had a different meaning to what providers are doing today. How will - how should - people in 5 or 10 years moderate websites and consume content? I'm not the greatest expert on the Internet, I started using it at approximately the same time that section 230 was passed, but I'm very familiar with it and that would be a really hard question for me to answer. A senior citizen who formed and solidified most of their ideas about the way society works or should work three to five decades ago would have a really hard time wrapping their mind around the concept even with excellent guidance from the best attorneys.
We need judgements that put our society in the best position for the next decade, and these 9 people may not be sufficiently able to be coached to think ahead far enough to do that.