Why is there only one charging port on these cars?
For the amount of time it takes to charge the car to a sufficient level, one charge port is enough. Adding a second or third charge port will only slightly reduce the fill-up time. The cost, complexity, etc. outweigh the small time savings.
Wouldn't it make sense to have multiple ports leading to multiple battery packs and the charging stations multiple cables to service those ports in order to reduce the time needed to charge?
Why not do the same for ICE cars? Fill your gas tank in 6 minutes instead of 7.
Because isn't part of the time needed to charge a battery pack related to how much capacity you're trying to charge?
Yes, but also how well the battery management system can handle the current, the temperature of the batteries, and the ability of the car to regulate that temperature, and how "full" you want to charge the batteries. Tesla recommends charging the batteries to 80% capacity for maximum battery life. I can charge my car from 10% to 80% in about 15 minutes at a supercharger. And that is plenty for everyday driving. When using a supercharger, the last 10% takes the longest to complete.
So that if you're trying to fill up one big pack doesn't that take you longer than trying to fill up multiple smaller packs?
All electric cars use many smaller packs, not one big battery. Tesla batteries look like AA batteries (18650 cells), but there are thousands of them. They are all monitored and controlled by the BMS. If I understand it correctly, not all of the batteries are getting charged each time. Some get charged more than others, but the 80% capacity is still reached.
Would it make the design of the car (or charging station) too complex and therefore too expensive?
Yes.
Would it be asking too much of consumers to plug in four cables instead of one?
Also yes. I rarely have to charge away from my house. I've used the supercharger only twice, I think. Saving 5 minutes of charging time just isn't a factor for me.