Why Bisexual but not Pansexual?

Why Bi and not Pan?
I’d thought I’d clarify the two, and also discuss why I identify as Bisexual, rather than Pansexual. The Bisexual+ umbrella should encourage both Pan’s and Bi people to work together and to combat erasure (instead of fighting amongst ourselves). To this day, Bisexuality is still misunderstood.