Well, there are plans and there are plans.
For some there are actual route adoptions, and perhaps even construction plans. Whether those plans will ever be funded is a different question, with the answer being "probably unlikely". For others routes have never have been nor will be adopted, and the routes have just never been removed from the state system.
Why haven't they been removed? A second good question, with the usual answer being some right of way had been purchased or some property, and it is more trouble to Caltrans to process that land to rescind and turn it over to another agency. The more common answer, however, is that a route on paper with no adoption doesn't affect anything, and isn't worth the legislature's time and money to remove from the books (which has significant cost given committees, votes, and the legislative process). As a California citizen, I'd rather them spend their money on something useful.