Are standalone dominion sets (Base, Intrigue) sold more often than expansions?
Why are there not more Expansions shipped with the base material (Copper,..., Gold, Estates, ..., Provinces)?
The initial plan - of RGG's - was to have all expansions standalone, every set coming with base cards (there were no small expansions).
But when Intrigue (way back when) was announced as coming with base cards, a lot of people on BGG complained. Well Intrigue having base cards lets you go up to 6 players, so there was that to defend it. But RGG announced, okay, the other expansions will not come with base cards. And they haven't.
There's no good way to evaluate impact on sales; we would need a set in the middle there that was a standalone, and don't have one. Mostly the earlier sets sell better than later ones, and large sets sell better than small ones. I could speculate as to why but so could anyone.