The reason is that alt text is scraped in order to train multimodal text + image models.
But for anyone who actually listens to the blind community, it doesn't take long to learn that these models are pretty important to a lot of people for accessibility. And regardless, alt text is directly helpful. I'm happy to put my displeasure with big tech on hold for things that genuinely improve people's lives.
This is how far you'd have to go to actually stop it from happening. Or at least you can't post *publicly* without it happening.
This is not to say that it's right for that to be the case, or that it's the individual's responsibility to curb bad behavior from these corporations. We need laws for that. But if people are going to take it upon themselves to disrupt this behavior, picking on alt text in particular is severely misguided.