The fees they charge third party sellers are significant.

Yes, and the cost to reimplement the USPS so that you can get your order in a day is also significant.

The case maker HYTE calculates 25% as net margin for brick and mortar stores for MSRP and says stores are tough and won’t allow any % less margin.

Update: oh and they also said stores won’t lower it because of the tariffs, making the stores more money.

That's gross margin, not net margin. It's not free to do the logistics to actually get you your order, either keeping warehouses and paying for shipping and handling, or physically maintaining and staffing a storefront to sell the product.