system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are avocados so expensive at fast food places?

I live in Southern California and there are tons of avocado groves all over the area yet almost every fast food place I go to (Subway, Chipotle, etc.) charge an extra $1.50 just to add a couple slices of avocado. Is it because they know people want it, they go bad more quickly, they're just greedy..?
gpt
Because they are expensive to grow, and all food will be more expensive at restaurants than at the grocery store. 

Avocados are also not a default item. They are not liked by everyone and they spoil very quickly so they charge more to cut their losses to spoilage. 

Those that like them are willing to pay extra for the luxury addon.