Why does this stream (and other streams) have the popular ones get the most upvotes while the new ones only got a few or none?

Probably because they stay on the front page for longer

It actually depends on what the owner sets the default to. For example, streams like the Undertale stream, RP stream, etc use new as the default order, because both of these streams are more focused on user interactions, kinda like forums, while streams like the fun stream are more like traditional social media, therefore sort by hot by default