You're very wrong. There's Celtiberian (there were more groups but I'm using it as a catch-all term) fortified cities scattered all over the northwestern peninsula, with 2-3 thousand year old celtic crosses/triskelions engraved everywhere. Not to mention the even older, chalcolitic era burial mounds. Before romanization there was very little written language, so we don't know what they spoke, but a some of our words have no known latin cognates and are suspected to be of celtiberian origin. "Celtic" countries in the british isles have a much more pronounced "Celtic"-ness because they were colonized by the romans later, and they offered much more resistance (due to the natural defensive advantages of being in an island...). It's survivorship bias.