There actually can be bs from a manufacturer where a site cannot list an item below their MSRP so in order to do a sale they have to do the bs like “add to cart to see price” or making you sign in. Sure sometimes it’s not an amazing deal but it can often be the lowest price you can find an item because they aren’t allowed to advertise a price that low.
Edit: See comment below to learn about MAP “minimum advertised price” which is different from MSRP “manufacturer suggested retail price” leaving my above comment alone with its inaccuracy so that the below comment continues to make sense and you can learn as I did.
MAP (minimum advertised price) is often different from MSRP, but otherwise this comment is correct.
In some industries, like RVs or auto parts, the vast majority of products have a MAP. The manufacturers also have bots that scan the internet for MAP violations, and they’ll blacklist a vendor if they don’t fix the price within a day or two. (Which is really annoying when there’s a false positive and I get blamed for it.)
I think it’s partly so high volume vendors can’t put smaller vendors out of business by just reducing their margins as much as possible, and it’s partly because the manufacturer doesn’t want their products to look like they’re really cheap. Customers feel better about finding a “great deal” on an “expensive” product.