It is a common term in concurrency and parallelism that refers to a specific kind of task [1]

[1]http://en.wikipedia.org/wiki/Embarrassingly_parallel

Because being good at embarassingly parallel problems is not something to be particularly proud of - the real, hard problems (for which the supercomputers are needed) can't be so parallelized, and the performance & quality of such systems depend on how well they can handle problems that need much more interdependencies between computing nodes than bitcoin.

"Embarrassingly parallel" is a term used to describe problems that can be easily divided amongst processes and require little to no communication between processes.

Because the payloads are tiny and require almost no coordination compared to many algorithms.

Machines take small work packets and crunch numbers, then pass back results in minutes. For many clusters, various steps of the algorithms require fast messaging for things like MPI.

TL;DR Bitcoin: no coordination during work