The cause is the whole thing, cost of shipping (container, gas, etc), cost of components (RAM, SSD, etc), cost of tariff, cost of lobbying and lawsuits, and overall inflation cost.
You can fit about 8,000 MacBook Pros into a 40-foot container in their retail packaging. If the cost of shipping a container went up by USD8,000 (a very large amount), that would be about USD1 per MBP. It's not the shipping that's driving the price increase.