2 things:

1. You create the data in whole. It is signed, so your own computer could be the server if you want and it still shows up on your friend's client. Platforms like X take your content and present it on their apps and lock it down so that Mary can't show fake content as if Matt wrote it. With signatures, Mary still can't do it and we don't need to trust X to protect us.

2. Your data can be sent to many servers. We already know they can't create fake content or modify your content, so all they can do is delete it or withold it. Sending it to many computers is better than just one in this regard.

3. I'll say it again, nostr is different because you can trust your own computer. If you do that, then it is nothing like cloud. Yet because nostr is a protocol, not a closed platform, you can be part of nostr, you don't NEED to trust another computer and people can download your content on their computers and not trust your computer etc. (Although it does makes sense to trust the computer of the author of some content.)