“Made on the same assembly line means it’s the same product” is a myth from people who have no experience in manufacturing/sourcing and are just mad about inflation and do not have a professional interest in the product. The specs are rarely the same. There are often typically significant differences in material, tooling, QA/QC, and warranty. Yes, there are plenty of examples where the upcharge is not justified, but it’s neither the rule nor the exception. It varies wildly across the market. I have my places where I buy premium, I have my places where I buy bottom tier.

For the common end user of household products, the closest they’ll get to understanding this is buying the Amazon, Alibaba, or Temu “version” of something. There will be a dozen differences that make the product worse. Maybe that’s fine for your use. If you think all toothbrushes are the same, try the free ones from a hotel. The handles are small, weak, and usually have sharp mold parting lines. But sure, they were likely made at the same place that made the $6 Colgate because the bristle-placing machine is the most important part of the process.

Meanwhile, towards the other end, a casual household end user will likely never exceed the capability of a hardware store wrench, so they’ll think it’s insane to pay more for a Snap-on at 4x the price. But it makes a difference to someone using and abusing it 8x a day, depending on its function to get paid. If it does break, the warranty replaces it immediately. Lifetime warranties from non-professional brands are notorious for stating it’s the lifetime of the product, not your lifetime, and it expired when it broke or wore out.

At the extreme end would be something like aircraft parts. The “same” bolt at the local store is 1/20 the price. But the aircraft bolt is a higher grade (more expensive), has much tighter tolerances (more money spent on control, higher scrap rate), has backing traceability documentation (money spent on labor and tracking systems), and is likely checked 100% to dimensional spec (money spent on labor and time). You could find the same bolt at the store. You will find a bolt that’s almost the same. You may find a bolt that’s completely wrong. None of that uncertainty is allowable in an aircraft bolt. Those “minor defects here and there” like your toothbrush claim are not acceptable, so systems must be in place to prevent them from escaping. You order a bolt, you get the bolt you ordered. Hundreds of lives depend on it.