Arso,
The Raavad is talking about who is a min. I can’t answer for others why they believed what they believed.
For me it’s very clear from the Torah, that Hashem has no guf.
I mean if you have an explanation how someone can believe Hashem is corporeal from the three examples I bought then go ahead and tell me.
How can Hashem have a guf if He was in existence before He created the universe/matter was created?
How can Hashem have a guf and be in the heaven and on earth at the same time?
How can Hashem have a guf when a guf has form and it says in the pasuk that Hashem has no form?