Probably because systems that passively do their job tend to be preferred. Also a battery would only last so long. IIRC DRAM needs to be constantly refreshed,

Probably because systems that passively do their job tend to be preferred. Also a battery would only last so long. IIRC DRAM needs to be constantly refreshed, so, it would be a trade-off between capacity and duration. Optane seems[1] to be 20~30X slower than DRAM but 4~10X faster than server SSDs [1]: https://superuser.com/a/1195674/187732 https://superuser.com/a/1195674/187732