Let's be honest, the leads in those movies didn't have the star power of Brokeback Mountain. We really haven't seen A-list actors jumping into roles as gay romantic leads. Most of them either aren't comfortable or simply don't have the balls to risk doing what Gyllenhaal and Ledger did. Even at that time they were already well-established, and both have been creatively fearless throughout their careers.
And then there's the fact that those parts simply don't exist. There's obviously been some progress, mostly on television, but none of these films were produced for mainstream theatrical release and all premiered at Film festivals followed by limited release, including Brokeback Mountain.