When we started developing this product last year, we looked at price trends and performance data on DDR4 vs DDR5 and made the bet that DDR5 would have both price and availability issues in 2022. That has turned out to be the case, with DDR5 SO-DIMMs typically going for 50-70% over the equivalent DDR4 capacity, without delivering performance improvements to justify that premium. This is something that will improve in the future, and we'll continue to track this for future products.
They sell to different audiences though, so maybe optimize for different outcomes. I'd imagine DDR5 is much easier to sell to a "pro-sumer" who games on Windows vs. to a programmer who runs linux and can make an educated decision re: price/perf tradeoff.
Why no DDR5?