His thought process was:
"I wanna use the spider lady demon for BM, so I can draw her naked upper body and sell more merchandising. But the Flying 6/Calamities are themed being Ancestral Zoans, not mythical. I KNOW, I'm gonna draw her like a SMILE and fuck y'all".
Lmao for real. That's exactly what happened. He didn't even give her a canon zoan form this whole time. Was she in hybrid the whole time then too? The drugs she took were a Smile? But why can the spider breathe fire? Did Queen modify her? But then again, we've seen other unexplained fire powers.
(Cries in YEARS of waiting for Oda to truly explain Diable Jambe, why Zoro could use blue fire vs Ryuuma and Luffys fire powers too. I guess Luffys is from his Myth Zoan though ofc?)
Funnily enough I just randomly watched this earlier too:
There was some badass fanart of Maria being a giant snake instead, Titania as one example or Black Mamba and Rivin was facing her too, all way before her actual DF reveal and Robin fighting her too.
Also Maria's zoan, the spider she is based on, grew to a mere 1 millimeters at most IRL apparently! It should almost be invisible to the naked eye at least then?! (pun not intended lol)