True, also... in fact, some of that creativity is either shared with players or within the scope provided by *HOW* the gameplay was designed by Stardock.
By this, i mean - they allow modders to alter some features on the premise that it might enhance their product value and that it all stays inside reasonable "limits" - assuming no Copyright infrigment is involved.
Ever heard the term "Foxed"?
The filming corporation would sue all azimuths for anything nearly ressembling what they had on distribution (Lucas' Star Wars, being just one of many more, btw) -- in the end, they realized the activity was beyond legal actions that enriched only Lawyers.
The whole gaming industry can protect its assets, given.
But try to pay for a minute of publicity during the SuperBowl - and you'll understand what sort of indirect business boost a single MOD (of both quality & popularity) can mean to "longevity" of a title.
Property is also hard to prove if only from derivation than from outright "copying".
Jordo21 plagiarized and yet, who hasn't. X-Worlds included, btw. Could Mythos or Microprose sue me for using X-Coms? I doubt it, cuz whomever still has those rights (if any, btw) will be thankful that the franchise remained somehow popular for all these years since the originals were created.
Even in your own BoL, there's got to be source material.