Yeah but that's the whole thing, we almost never try hard to overload stuff. It's the slow creep that gets you. You add a few more cans to the garage shelf, then some paint, then a toolbox, and you've doubled the weight without noticing. I see it with cheap furniture too, people trust it way past its limit because it hasn't broken yet. It's not about engine blocks, it's about not respecting how all those little things add up over time.
Honestly how much weight are people really putting on these things? Most garage storage is light seasonal stuff or old clothes. Seems like you'd have to try pretty hard to overload a decent metal rack. Maybe some people are stacking engine blocks up there but for normal use this warning feels overblown.
People treat weight limits like they're just a suggestion. My old roommate filled a cheap bookshelf with vinyl records, swore it was fine because it hadn't collapsed yet. That's the same mindset, trusting the thing until it gives out. It's not about the single heavy item, it's about the total weight of all the normal junk we keep adding. The warning isn't for the careful person, it's for the rest of us who stop paying attention.