Cause it's crap
It's not worth the cost and delivers the same performance as a SAN. They're up to a just over a gig (iirc) and can only be used in RAID 0 or 1. In a database setting you'll still need to replicate your db to a DR site which means you have to go back to mirroring or log shipping which is far more intrusive on the server than SAN replication.
p.s. Yes I do regret putting tempdb on a couple of these.