In the original series, the Egyptian gods remained as they were, and later in the very same series a set of cards is called the Nordic gods; what makes the Earthbound Gods so different?
I don't really follow Yu-Gi-Oh anymore, but I think this can be explained on purely linguistic grounds.
Leaving Obelisk (and "Slifer") aside for a moment, Ra and Osiris take as their namesakes beings that we, in English, call gods. Ra is "an Egyptian god" because he was worshipped by the Egyptian people, and the same is true of Osiris. So we call their Yu-Gi-Oh counterparts "the Egyptian god cards".
Likewise, we conceptualize Loki, Odin, and Thor as "Norse gods" because they were worshipped by pre-Christian North Germanic peoples, and so we call their Yu-Gi-Oh counterparts "the Nordic god cards".
But do we call the figures drawn in the Nazca lines "gods"? No, we do not. Perhaps the Nazca people who created them did worship them (though it's difficult to tell, given that they produced no texts), but we - the target audience - think of them as "just" a spider or a bird or a tree, not as targets of worship. It would, in my opinion, be weird to use the word "god" to describe the Yu-Gi-Oh versions of these Nazca figures. I suspect that whoever made this translation decision followed a similar line of thought.
I hardly think this has anything to do with censorship. If they cared about not offending monotheists, well, that boat sailed long ago.
(It is perhaps worth noting that though the Japanese word 神 kami is typically translated as "god", there isn't a one-to-one equivalence here. The English word is heavily colored by the Christian sense of capital-G God, while the Japanese word is colored by indigenous worship practices that treat a wider variety of entities as kami. Just because the Japanese name of the Nazca figures is 地縛神 jibakushin, that doesn't mean that the "correct" translation of it must involve the word "god".)