While as a user it sucks that is exactly the reasons people do it. It takes the value away from reddit, if the content that users want to see it not there people will not go there.
What I find the best compromise is users that take their comments they had on reddit and post them again as it’s own post to lemmy with the context needed. While not perfect the information is at least not lost completely and a google search in the future might actually bring someone to a lemmy instance instead of to a corporation like reddit. But that is obviously a lot of work to do, especially if you have lot of helpful comments on reddit.
As I posted in response to another comment along these lines: