(1) CA is much better positioned to straighten out the land use issues. It needs to use the existing I-5 right of way, it needs to tunnel through some mountains, and it probably needs to eminent domain some additional bits of land for pylon bases where I-5 curves too sharply. No matter what, this is a project that has to pass the legislature in order to get built.
(2) A CA-sponsored bond issue must be by far the lowest cost way to finance a $7B infrastructure project that's amortized over 30 years.