Neocities has put measures in place to prevent hotlinking of content from non-Neocities sites. This is a part of our process to improve the performance of Neocities web sites, provide more free space for our users, and ensure the site's future sustainability.
Hotlinking is when a non-HTML file hosted by Neocities is embedded into another site that is not hosted by Neocities.
We don't allow this because the purpose of Neocities is not to be a "file dump", but to be a portal for people creating their own web sites. When Neocities is used as a file dump for other sites, it hurts Neocities sites by cutting into the amount of bandwidth available to them. We want to focus our resources on those sites.
If you have a web site on another server, the best way to serve files for it is by putting those files directly on that server! Not only does this ensure that the files will not disappear in the future, but it also makes it easier for you to backup that site independently. There's really no good reason to use Neocities to host files for other web sites.
If you need to store files for hotlinking use, there are plenty of alternatives. Imgur for example is a place you can store images that can be embedded by any site. Again, this is bad practice because you have to trust Imgur to not delete the image in the future for your site to continue loading. You're still better off hosting the images on the site's own server.
Please keep in mind that our reasons for doing this are purely out of requirement. We need to focus on being sustainable to run Neocities without advertisers and stay independent, and preventing Neocites from being used as a "file dump host" has always been a part of that process.
The hotlinking policy currently applies to all free sites, however you can remove the hotlinking policy by upgrading to the Neocities Supporter Plan. That said, for the philosophy reasons mentioned above, we still strongly recommend that you don't use Neocities for hotlinking to other sites.