It's really not that hard to make these (although your exterior is okay).
This isn't just a basic keyboard with a changing screen. Unless you have looked at the internals and can appreciate the process of creating ROMs, I think you are basing that statement off the very simplistic creations that were around years back which don't do this model justice.
I think people believe they can easily make builds that look like computers in Blockland, but the process of building a BLPC is quite different.