I think we're missing the main point of pen names. In the cases referenced, someone changed their SOL ID, rather than their pen name. This is often done when someone decides to abandon a pseudonym and write under their own name.
What happens more often, is if an author writes a different kind of story, and doesn't think his regular readers will appreciate it, or wants to appeal to an entirely different market. Thus if someone writes romance stories, and decides to try their hand at horror, they'd create a separate pen name to keep their reader bases separate. Or, if someone normally writes normal romances, but decides to write a gay romance. His regular readers might not respond well to that, so he'd create a separate pen name just so his other stories wouldn't take a beating from the homophobic one-bombers.