I suspect two reasons: 1) This summarizes a large amount what other people were thinking. Note that the post Gwern is replying to has had a lot of downvotes, so people who think it is obviously not well thought out favor a response like this. 2) Gwern is a highly respected user who almost never says something without fairly good data to back up his positions, so they are operating under this being a summary of Gwern's more detailed position. (A slightly more cynical version of 2 is simply that Gwern has high status here.)