If I had to guess, probably because you could get equivalent performance cheaper with standard servers. Plus, there's a good chance that your distributed solution could fit on a single server, removing the overhead.
Yep. If you compare a $1,000 Xeon E3 server with a $1,000 cluster of ten Minnowboards, the E3 will deliver more performance. Likewise, a $10,000 E5 server beats a cluster of E3s in many cases.
