Actually, you don't have to. You just want to.
N=1 but to me, LLMs are a perfect example of where the "ideology embedded into the GPL" benefits the world.
The point of Free Software isn't for developers to sort-of-but-not-quite give away the code. The point of Free Software is to promote self-sufficient communities.
GPL through its clauses, particularly the viral/forced reciprocity ones, prevents software itself from becoming an asset that can be rented, but it doesn't prevent business around software. RMS/FSF didn't make the common (among fans of OSS and Free Software) but dumb assumption that everyone wants or should be a developer - the license is structured to allow anyone to learn from and modify software, including paying a specialist to do it for them. Small-scale specialization and local markets are key for robust and healthy communities, and this is what Free Software ultimately encourages.
LLMs becoming a cheap tool for modifying or writing software, even by non-specialists (or at least people who aren't domain experts), furthers those same goals, by increasing individual and communal self-sufficiency and self-reliance.
(INB4: The fact that good LLMs are themselves owned by some multinational corps is irrelevant - much in the same way as cars are important tool for personal and communal self-sufficiently, despite being designed and manufactured by few large corporations. They're still tools ~anyone can use.)