FAQ:How can I use the asset downloader to download everything by everyone?
In the asset downloader you can download one item at a time. That you cannot do batch or mass downloading is by design, and a way to protect the limited capacity hosting we're able to pay for.
The MakeHuman project has a very, very limited budget (you can see exactly how much by going to the patreon page). This is enough to pay for the already pretty heavy load caused by the asset downloader. It is definitely not enough to pay for the kind of hosting that would be needed if thousands of users started to mass download everything in the now pretty large asset repository.
So for the foreseeable future we will not be adding features such as selecting multiple assets to batch download or a download everything functionality.