The series is set during a time when divorce was scandalous (possibly too scandalous for TV), so divorce really isn't as much of an option for Alice and Bob as the audience (especially a modern, Western audience) might be led to believe.
Bob and/or Alice are would rather stay married than spend their money on a divorce or don't have enough money for a divorce.
The series makes it clear that although they're attending couples' therapy, it isn't working and a trial separation led only to a Green-Eyed Epiphany. Alice and Bob are still anything butHappily Married, and they should have just gotten a divorce.
Alice and Bob divorce. Cue Bob lying alone in bed, asking, "Now what?" and hearing only crickets in response.
After the divorce, Bob's friends throw a "reverse bachelor party" in Hawaii in an attempt to lift his spirits...which (among other things), involves Bob water-skiing over a shark.
Defied: Alice and Bob decide that they are going to look at the divorce as a new beginning, not an ending, and take advantage of the opportunity, even though it means stepping out of their comfort zones.
Discussed: "If Alice and Bob are so miserable, why don't they just divorce?"
Conversed: "Well, for a series focused solely on Alice and Bob and playing their Awful Wedded Life for every laugh it's worth, it would kill the premise, and there's no guarantee a Re Tool would be more compelling for the audience."