Tiered Shipping

I don't like the options currently available for me for the following reasons:

Free shipping: I don't have lightweight items.  Free shipping would either jack up my item price too high or cut into my profits too much

Flat rate: It's fine for one item, but it essentially discourages a customer from ordering more than one item as shipping costs for three items are always less than triple a single item

Calculated: is the most accurate, but it requires me to calculate the size and price of every product I have.  My products are too varied for me to waste time with this.

Included in the description: Just a combination off all of the above

Tiered shipping costs is available on Walmart, Amazon, Shopify, and every other major platform.  Why isn't it here?