The Reuleaux triangle is for some measurements (for example material used), more optimal than a circle, while still able to roll smoothly.
If the wheels on each end of an axle aren't perfectly aligned the up and down motion won't be the same on each side. The speed of the up and down motion while moving down a modern road would be very fast. This would wear our parts far more quickly.
Theory and practical implications don't always line up. In practice it's not more optimal when applying to every day real world application.