Alt text for blind and low vision users
Alt text for low bandwidth users
Alt text for flakey Internet
Alt text for digital decay and link rot
Alt text for text based browsers
Alt text for calling out the relevant details you mistakenly assume are obvious to everyone
Alt text for explaining the joke to people that don't have the same background as you
Alt text for the 10,000 people learning something "everyone knows" for the first time today
Alt text for leveling up your own writing skills
Alt text for everyone