Just because something is proven and shown to be true doesn't mean that it's always practical.

The proof can be entirely valid even if it's not actually reasonable to implement and requires an enormous size lookup table - but it still is a meaningful mathematical result and makes progress.

I'm sure there are plenty of times where originally something was proven and thought to be completely impractical but then later had niche use cases or was the bedrock for solving other cases. And the opposite is true: there remain plenty of proofs of things that are mathematically certain but will in all practicality never be useful.