Why would a lawyer motion to withdraw as counsel and say that further representation may create the appearance of an impropriety at the least if not an actual conflict of interest for myself?

There can be many reasons. If, for example, your lawyer had other clients who had the same or a similar claim as yours against the same defendant and there was concern upon acquiring a judgment as to the sufficiency of assets owned by the defendant, the lawyer could not take further action to collect or execute upon the judgment without prejudicing the other client. Likewise, if the other client wanted the lawyer to chase his judgment or perhaps to file a bankruptcy, the lawyer could not do so without prejudicing your interests. In such a case the lawyer might have to withdraw due to conflict of interest.