From what I remember because carbon is a very weak atom, carbon could form an ionic bond with something but this would require an alkaline to have a stable 8 because octets in their nature are unstable, if not the bond just becomes unstable and breaks. Also you're talking about the earth found substances of carbon which usually isn't C2 but in forms of Co2, CH4, etc. So it makes electron "giving away" harder because it's already "bonded" with some other element
Elements can only loose upto 3 atoms. but carbon is a tetravalent . but no element can give 4 electrons. even carbon element itself cant do that. so to form bonds it goes for covalent bonds where electrons r shared among but atoms. hence it doesent go for tranfer of electrons.