That is a fair point.

Personally in an ideal world, I would like to export all of my data from reddit before leaving, and then if later someone wants to host all of the dataset under a permissive open source license like I believe stackoverflow or wikipedia do, which is accessible to search engines, then scrub+anonymize my dataset and upload it there.

Obviously the issues with something like this are people uploading doctored data to poison the training models etc.

I can’t speak for op but one reason I’ve seen mentioned is users don’t want reddit to keep historic data. Reddit will profit from that data by selling it, using it as corpus for training etc.