1 To have communion with other Catholics outside the sedevacantists
2 To fulfill a necessary condition for my own salvation
3 Because the church has not officially condemned him yet
4 Because I dont have the authority to decide who is pope and who is not
1. Generally, the R&R folks refuse communion with sedevacantist Catholics. So I think no matter what you decide on the status of Jorge Bergoglio's claim to the papacy you are certain to not be in communion with at least some faithful Catholics.
2. It is true that you must accept a true Pope but it is also true that you must reject false popes. But if with a clear conscience you are mistaken one way or the other you will not be damned for that alone.
3. Canon 188.4: “Through tacit resignation, accepted by the law itself, all offices become vacant ipso facto
and without any declaration if a cleric: ...n.4. Has publicly forsaken the Catholic Faith.”
4. Dozens of Catholic bishops and hundreds and maybe thousands of priests have already publicly declared that Jorge Bergoglio's claim to the papacy is invalid.