It is said that in Hollywood you need a "pitch" sentence that sums up your show quickly for a producer, like "Jaws crossed with When Harry Met Sally." My guess is that Silverman is successful enough that she was able to just say, "I'd like to do something wacky starring me."
The result is something that, while not bad, is weirdly unfocused. At the end of the first and only episode of Susan 313, I was left unsure as to where the show was going or why it exists at all.
The series apparently planned to follow Susan as she recovered from the breakup of a long-time relationship as she reformed her own life. This is intercut with scenes of her explaining her life to some sort of focus group.
It's an unusual approach to breaking the fourth wall, but not an especially successful one. Much of the reason is it's just confusing. Is the snarky Susan talking to the test group supposed to be the same woman as the perplexed one moving back to her old apartment? They feel unconnected.
I've always liked Silverman, the show is sometimes funny and the supporting cast is solid, particularly Tig Notaro. Because of that, if the series had been picked up I probably would have watched another episode or two to see if it sorted itself out. But I think the executives who rejected this one made a good call.