If as the 'Crats and other politicians say, the Ukrainian conflict is "obviously" in our own best interests to remain involved and invest in further, it should be easy to articulate to the People. Why then haven't the 'Crats done so?

I think the answer may actually be closer to what detractors like Cornel West say is the motivation than what the war-hawks claim. 

IF neither side can legitimately claim a moral high ground - and it seems clear that Ukraine is a plutocratic oligarchy almost as corrupt as Russia's, then where is the morality of allowing both of them to press their own citizens into the meat grinder day after day? TO SUPPORT THE BEST INTERESTS OF CORRUPT BILLIONAIRES!?! 

It may well be that many (most) of the Ukrainian people are deceived if they think they are fighting for a better life for themselves by supporting their current government. By giving endless, unconditional, limitless support to the Ukrainians, we encourage them to cling to even a remote chance they will prevail in some sort of decisive victory instead of negotiating peaceful end to the conflict. 

Where the oligarchs eventually draw their imaginary borders may mean less than how many innocent men, women and children will remain alive and have a chance to live a normal life again if the fighting stops through granting concessions and accepting something less than what they feel they "deserve".

Tzadkiel (the god): (rendering judgment) I will make a judgment, though it cannot be just. 

The above is a quote from author Gene Wolfe. The character Tzadkiel is a god who is rendering judgment upon Earth. One side wants him to destroy the human life on the surface (with a flood) and let it be reborn anew.,The other wants to allow Earth to continue to try to achieve Utopia, though it is by all appearances completely corrupt on every level with equally corrupt, eternally-warring factions. His statement is that no matter how he judges, neither side can possibly get everything they believe they morally deserve, and so justice (equitable adjudication of conflict) in any absolute sense, is impossible even for a god.

Tzadkiel eventually destroys Humanity on Earth to be reborn (rather than to stumble onward into evil, savage decrepitude) and remade as pure, unspoiled Ushas.