Crystal shrimp are much more expensive than cherry and ghost, along with a higher need for ideal water conditions. Generally, only dedicated and experienced shrimp owners consider spending the money to keep these, and this forum is mostly for Betta owners, hence the less mention.
Bettas tend to attack and kill shrimp occasionally as well, and so say goodbye to $10 (or more) for each crystal shrimp it gets...
The forum thread documents a serious shrimp hobbyist who used two 20L tanks for shrimps, including crystals. Browse through there for some interesting info on these beautiful shrimp!