I have been wondering why the USCCB does not include Intrinsic Evils as issues in their statements on Social Justice, or do they? Have I missed their statements on these issues? If I have, why do over half of the catholics in the US disregard their directives when voting? Lack of catechesis, or what?
First of all, I think that it is important to call one thing in mind: the USCCB’s declarations on social justice or issues regarding intrinsic evils (such as their voting guides) have absolutely no force of law (unless the decree or publication has been ratified by the Holy See).
Can. 455 §1. A conference of bishops can only issue general decrees in cases where universal law has prescribed it or a special mandate of the Apostolic See has established it either motu proprio or at the request of the conference itself.
§2. The decrees mentioned in §1, in order to be enacted validly in a plenary meeting, must be passed by at least a two thirds vote of the prelates who belong to the conference and possess a deliberative vote.
They do not obtain binding force unless they have been legitimately promulgated after having been reviewed by the Apostolic See.
§3. The conference of bishops itself determines the manner of promulgation and the time when the decrees take effect.
§4.
In cases in which neither universal law nor a special mandate of the Apostolic See has granted the power mentioned in §1 to a conference of bishops, the competence of each diocesan bishop remains intact, nor is a conference or its president able to act in the name of all the bishops unless each and every bishop has given consent.
In other words, the statements made by your bishop in regards to the territory of your particular church has importance (again, provided it lines up with the Universal Magesterium). Such a statement can be considered binding if given in an area within his control. But any statement issued by the USCCB, unless it has been given a recognito by the Pope, should be taken as strictly advisory. (Naturally, your local bishop can adopt the positions as his own positions…)
You would do far better, in regards to political issues, to refer to the 2002 CDF document,
The Participation of Catholics in Political Life, and take a look not only at that document but the documents it references in its footnotes. That document has more legal force than anything issued by the USCCB on the subject.
As far as the voting habits of individual Catholics, the most charitable rationale I would give is that it is due to very poor catechesis on their parts.