system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can’t airlines pay to keep their airplane slots, without having to fly empty planes?
gpt
The intend of the rule is to prevent wealthy airlines from just buying all the slots of an airport and then not actually using them.  
Preventing smaller airlines from competing and passengers from actually flying.  
Ofcourse the rule has problems when demand drops way below capacity, but chaning rules in big organizations is often very slow, so in the meantime airlines have to do empty flights.