I would bet that's because there are a large number projects that got written in Haskell/Rust by someone looking to learn on-the-job, for a highly non-technical business. Now anyone hired to implement new business capabilities is inherently locked in to "low-ROI" work, short of convincing the business of a big rewrite in a new language (unsurprisingly impossible)... and they'll probably get someone else looking to learn the language on the job :)

Then there are HFTs with valuable and effective software, which can fully exploit the skills of an advanced engineer to quickly make the company 10x+ their wages - naturally such jobs pay a bit more.

Jobs basically pay based on the rarity of the skill set and the profit capital owners can extract from the laborer.

Don't "invest" in a rare/difficult-to-acquire skill set which is not profitable (but also, don't assume life needs to be an investment - we only have the one :)