Those widening projects are almost always paid for with federal highway money. State gas tax covers most of the "local match" - usually about 20% of the project cost but sometimes up to 50%. The federal funds in particular get allocated by the Metropolitan Planning Organization - SCAG for San Bernardino County (and basically all of SoCal other than San Diego County), and the state itself for Inyo Co. because there's no MPO, with some involvement from the Regional Transportation Planning Agency (part of Inyo County), for the Olancha-Cartago segment. In theory, the federal money comes from gas tax too, but in practice, since the federal gas tax hasn't increased in a long time (despite inflation), a lot of the money is from the general fund through one of the periodic federal transportation acts.

All of which is to say: it's political, and there's never enough money to go around. Many projects have to wait many years from original proposal to actual construction. And at the federal level rail (e.g. Amtrak and transit) improvement money comes out of the same pot.

I'm pretty sure I saw some very preliminary stuff for Olancha-Cartago back when I worked for Caltrans, probably 25 or more years ago.