another thing with the fewer numbers of main female characters is that one has less choice of pairing types that might hit one's buttons (e.g. villain/hero, or the best buddies).
How much that affects people's shipping depends on the kind of shipper you are, I think. With het and slash pairings, there are often plenty of fans willing to project their favorite dynamic onto whatever pair of characters comes closest to it and/or is prettiest or possess some quality as individuals that hits them in the Id. If you fall on the "I need the pairing to jump out at me from canon and grab me by the Id" side of things, though, yeah, it can be harder to find the kind of pairing dynamic you like between two women who are also in a canon you like. (Marvel's better about it than a lot of other fandoms, because even though they treat their female characters horribly, they have a much wider variety of them simply because the Marvel-verse has so many characters).
no subject
How much that affects people's shipping depends on the kind of shipper you are, I think. With het and slash pairings, there are often plenty of fans willing to project their favorite dynamic onto whatever pair of characters comes closest to it and/or is prettiest or possess some quality as individuals that hits them in the Id. If you fall on the "I need the pairing to jump out at me from canon and grab me by the Id" side of things, though, yeah, it can be harder to find the kind of pairing dynamic you like between two women who are also in a canon you like. (Marvel's better about it than a lot of other fandoms, because even though they treat their female characters horribly, they have a much wider variety of them simply because the Marvel-verse has so many characters).