Another reason we should not let the receiving server resolve a link preview (so apart from the ddos that is many receiving servers at once loading from a site, bringing small blogs down): your text in the preview will be in the language of where the server is located. E.g. on mastodon.social previews are often in German.

If the client resolves the link preview, load will be spread in time and the reader gets the text in their language. If the sending server resolves the link (my preferred solution), only one request is done to the site (much fairer) and the text will be in a language the poster expects and can see.