You're missing the whole context about how React is a library with a huge enterprise sponsor (Meta) who uses it to build some of the biggest web frontends in the world (Facebook etc.) where most of their engineering talent, like most enterprises, will trend to be juniors in order to save money.
Juniors will not naively get the dependency array for useMemo correct, period. With enough juniors banging away on enough PRs, especially if PRs are not reviewed by the most senior talent to save time, this becomes a problem at scale. The need to introduce extra compilation steps, especially when a codebase the size of Facebook already has (I'm sure) distributed build caching, is more or less immaterial compared to the savings of getting more PRs to be correct when first raised for review.