@wimpy The replies to this are obnoxious. As @jwz has pointed out, this is a real problem, but lots of people are calling this person names, saying he should fix his site, to work around a wasteful Mastodon inefficiency. It's a bug and it needs to be fixed; we shouldn't be generating tens of thousands of requests to make the link preview. It could be generated once and the image could be shared, or it could be cached in some other way.
There is a workaround, sort of. When linking to someone's site, if an image is included in the post a link preview image won't be generated.