Hard?? Why would it be hard?? I mean for a sandbox you just need to create a (smallish) world.. Develop a system for interacting with the people you place in it.. Build a way for EACH of the NPCs stories to progress at 1 or often more locations.. Oops, forget that there needs to be a way to move between locations.. Add at least a bit of a overall story to make things interesting.. Umm, of course there are probably a couple dozen other things I've missed.. AND doing that without bugs.. Nope, I can't see why ANYONE would think that's hard.
So far THIS game has been interesting and I look forward to seeing how it grows. As to Sandbox stuff, take your time, do what YOU want, and add Chocolate Chip Cookies.
Just a thought.
P.S. Yes I was being silly/sarcastic with the first bit.