First of all: it's not compression. At least not in any meaningful sense of the word. The comparison is like calling deleting 99.99% of a file 'compression'. The bits just are not there. Second I'm not sure why people don't just... look up copyright law. You don't need to get that far into it to reach the fair use portion on wikipedia and find:

Amount and substantiality of the portion used in relation to the copyrighted work as a whole: Courts look at both the quantity and quality of the copyrighted material that was used. Using a large portion of the copyrighted work is less likely to be fair use. However, courts have occasionally found use of an entire work to be fair use, and in other contexts, using even a small amount of a copyrighted work was determined not to be fair use because the selection was an important part—or the "heart"—of the work.

In no way, shape, or form is a 'substantial' portion of any of these works included in the model. Given the model sizes and the amount of data used if it were any type of compression it would be the most impressive compression in the world.

But lets say you're still not convinced. What else can we find under fair use?

Purpose and character of the use, including whether the use is of a commercial nature or is for nonprofit educational purposes: Nonprofit educational and noncommercial uses are more likely to be fair use. This does not mean that all nonprofit education and noncommercial uses are fair use or that all commercial uses are not fair. Instead, courts will balance the purpose and character of the use against the other factors below. Additionally, "transformative" uses are more likely to be considered fair. Transformative uses are those that add something new, with a further purpose or different character, and do not substitute for the original use of the work.

AI Models are by necessity transformative. Even if you want to torture the definition of 'compression' to try to make it fit the model is still massively transformative. An AI model looks and functions nothing like the original works. Two out of the four major standards for fair use are inherent in the creation of AI models. Ironically the stronger argument against fair use is the effect on the market/value of the copyrighted work. There is a real risk of AI models pushing down demand for the works they trained from, however it's tougher to prove and no one wants to just say "I just want money" so instead we have these threads where people try to torture the definition of compression and don't just look up what is generally considered fair use.