How can we reconcile excommunicating those who abandon prayer with the permissibility of marrying People of the Book and eating their food, despite their disbelief due to their not believing in the Muhammadan message?

One who abandons prayer is an unbeliever, and their ruling concerning marriage is like that of a non-scriptural unbeliever. Although there is a consensus on the distinction between disbelievers and the polytheists among the People of the Book, Allah the Almighty has permitted marriage to chaste women from those who were given the Scripture. Allah the Almighty says: "This day [all] good foods have been made lawful for you. And the food of those who were given the Scripture is lawful for you and your food is lawful for them. And [lawful for you in marriage are] chaste women from among the believers and chaste women from among those who were given the Scripture before you..." (Quran 5:5). This is Allah's judgment, which no one can overturn.