Why didn't Gesher and Kulanu merge? It's my hunch that Levy would fit in well with Kulanu and their moderate-right-on-security, economically populist positioning.
The Knesset's basic law saysA Knesset member seceding from his faction and failing to tender his resignation as a Knesset member in close proximity to his secession, shall not be included, in the election for the next Knesset, in the list of candidates submitted by a party that was represented by a faction of the outgoing Knesset
Levy left Yisrael Beiteinu and sat as an independent in the Knesset rather than resigning, which means she cannot be included on Kulanu's list. Theoretically, she could choose not to run, in which case the rest of her list could merge with Kulanu, but that sort of defeats the whole point of the exercise.