A multitude of factors are considered when building a roadway system, and it can be a lengthy process.
Over time, factors that might have been more important in determining the original design may change, such as the southbound Broadway Extension/Interstate 44 interchange, which is undergoing a massive makeover that will take years.
In a large city, the amount of traffic and the routes motorists want and need are major considerations. Exits and entry points are no exception. Here's an example.
Traveling north on Interstate 235 the exit at NW 23 is very dangerous as traffic backs onto the interstate, even in something less than drive times. The reason is the way the two exit lanes allow traffic to flow. The right lane is for right turn only with the left lane allowing for straight line and left-turn travel. So many exiters wanting to turn left while the right lane in empty is the reason for the backup. The backup problem could be lessened if one could turn left from both lanes. It's not unusual for someone in the only left-turn lane to have to wait through more than one cycle of the light to make it to the intersection, but the most dangerous thing is when that lane backs up onto the interstate highway. Some common sense here would be very beneficial.
You're correct that that's an area that can really stack up, Tom. And the bulk of the northbound traffic does head west. But changing the flow there could pose even more problems.