Instacart shows you the final price. The price they paid for the goods is immaterial - you're choosing the convenience of not having to write your own delivery app, recruiting employees, or set up payment.
When you walk into a book store, do you demand to see the book price broken down into manufacturer's price, store rent, employee pay, and store profit and complain when the difference between the manufacturer's price and the retail price is too high?
It's the same reason I think mechanics are shitty when they charge 50%+ markup on parts for auto repair. I'm paying you for the service - the right thing to do is to show the cost of the service separate from the market price of the product.
Alcohol/food at a restaurant is different - it is clear and known that service and product are interwoven in the list price.
Now it could be something consumers DEMAND which would give a competitor an advantage if they did it (see Everlane with their transparent pricing) but it's not unethical or sleazy not to disclose the underlying costs of your goods.