system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does airfare go up in price the closer to the date of flight? Also, what accounts for the price dips and hikes that seemingly change hourly?

Why isn't a seat for a flight a fixed price? I don't pay more for tickets to say, the opera or a hotel the closer to the date i book my ticket.

That is my question. Thanks Reddit. I was born yesterday.
gpt
the plane leaves regardless of how many passengers are on the plane.  the pilot, stewardesses, the gate, the baggage handling are all fixed costs.  

now there's only 200 seats on the plane.  you're going to want to get the maximum money out of each and every passenger.  if you charge too max, you won't fill the plane to capacity.  charge too little and you'll miss out on potential revenue.   

the passengers that book early are planned trips.   there's plenty of competition to sway the passenger onto another carrier.   so the price is low to begin with to lock in those.    as the flight date approaches, the passenger profile changes from the people that would LIKE to go there, to the people that NEED to go there.  last minute business trips,  family emergencies, etc.   these passengers are willing to pay more as long as you get them to the destination.    so if they're willing to pay more, why not charge them more?