Notch did explain this on his blog. Basically, he didn't like the pressure that comes with working on huge projects when you've become a public figure. You can read his full statement at http://notch.tumblr.com/. I couldn't find a permalink, but it doesn't look like that blog is going to receive any more updates.0x10c subtract 80s style and 16 bit in-game computers = StarMade
It looks like they were aiming for a realistic tone, so I suspect that in addition to "creative roadblocks", they were probably running face-first into insurmountable simulation complexities.
Fixed that for you.Notch is a weakling who can't stop going on vacations. That's why he canceled 0x10c and sold Minecraft to Microsoft.