Then when you want to use the AT protocol without a webserver, you would have to set a DNS entry (CNAME) that points to a service like Bluesky. So for users without a web server, it would stay the same amount of work.
+ hosting the server + admin the server + securing the server + keeping the server up all the time
For trivially small amounts of data it seems a massive waste of time and effort.
If however, you are storing and verifying identity of 100's+++ of users within said domain then hosting that makes sense (pgp for email should probably work this way).
And for others it would be just
echo 'my metadata' | ssh myhost "cat > /my/web/dir/at_identity.json"