system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why don't more cars have doors that open upwards? They seem like they can use parking space more efficiently

Cars with doors that open sideways require more parking space, so it seems logical to me to have more cars with doors that open upwards. I don't imagine the difference in costs is high enough to be prohibitive.
gpt
They have more complex moving parts that are prone to take damage more often. They are much more expensive to install into cars and they are more expensive to repair and maintain. It is cost prohibitive.