Ehh, there are lots of way to gain 6 coin (or higher), let us not forget about Jester, Governor, Mint, Hoard and Haggler. Combos can, of course, let us do wild stuff: Forge/Fortresses -> free province; Expand (Remodel, Farmland, / Fortress -> free 7 coin card, Discard/Tunnel, Self-trashing (e.g. Embargo)/Market Square, and sundry other things all can hit.
So just gaining six coin in value isn't all that unusual. The bigger things are that gain goes on deck top (useful for setting up next turn or draw this turn in an engine) and that you can gain stuff that isn't gold. The problem is that "stuff that isn't gold" costing 6 doesn't end up in the Trash all too often. Sure, you might use the remodel family to put something to make a province, you might use the odd scaling TfB to hit something important, or you might use the upgrade family (e.g. Remake) to turn a 6 into a 7 .... but by and large you don't dump too many 6's into the trash. Even with cards like Procession, you normally want to keep most 6's in play, not in the trash. This distinctly lowers the utility of gaining up to 6 coin cards from the trash.
