Answer:
Let's look at the route between two major shipping ports, one in Europe (Hamburg) and one in Asia (Singapore).
Hamburg to Singapore via the Cape of Good Hope on the southern tip of Africa: 11,864 nautical miles
Hamburg to Singapore via the Suez Canal: 8,377 nautical miles
(A statute mile is 5,280 feet in length; a nautical mile is 6,076.11549... feet in length.)
That is a difference of 3,487 nautical miles. For the average ship steaming at 18 knots (18 nautical miles per hour), that's 193.72 hours or just over 8 days. So the Suez Canal literally saves over an entire week off of the transit from Europe to Asia.
That means money.
Less money that has to be spent on fuel to get the ship there, food for the crew for those 8 days not spend at sea, and less cost to shippers to send those good.
It also means more goods transported in a year, so manufacturers make more, shippers make more, and the consumer gets more and gets it faster.
Without the Suez Canal, everything increases in price. Not to mention the Cape of Good Hope is a notoriously dangerous shipping route with frequent and bad storms. That means not only does it take longer, but it's more dangerous.
A shorter route, a faster route, a less dangerous route, and a less expensive route. What's not to like?
(You can use this same analogy for the Panama Canal and transits around Cape Horn and South America)
