We as a society would rather swim across
Naheed Nenshi served as the 36th mayor of Calgary, Canada. One of his greatest accomplishments was completing the Peace Bridge of the C-train line, which apparently wasn’t such a great idea. One Twitter user was questioned why such an expensive bridge needed to be built in the first place.
The most obvious reason why they needed to build a bridge was for people to get across a river or lake. Actually, that’s really the only answer there is. As for why the government spent so much, bridges are expensive to build, but perhaps the OP had no idea. Now, he’s a bit wiser.