The spore drive, if it was just about using magic mushrooms in a special engine, I think people be like "what? oh, sure, like crystals in the other engine, like we use gas or something. Many of us fundamentally don't know how engines work so just putting something in that makes it go or mediates something that makes it go or somesuch, sure, I get that".
But it's not just putting spores into an engine. It's a special connected network that exists everywhere and ties the universe together, not an energetic force like gravity or a mystical force like The Force (old school SW), but more like The Force (new school SW midichlorian style). Something of substance that is everywhere.