I think the key difference to me (as someone who enjoys both) is that Rimworld is more interesting from a moment to moment standpoint, the sheer depth of simulation in Dwarf Fortress produces far more memorable events.

Put another way, I don't remember any specific events in Rimworld, but I'm more than happy to tell you about the dwarf who pathologically elected to engrave the walls of the fortress exclusively with depictions of a particularly delicious piece of cheese he ate.