Most peertube instances are pretty bad right now, so if one instance decides to follow everything else, that instance would be full of trash.

Also, as with a regular webpage, it doesnt make sense to link your instance to every other instance. Sure, by doing so, you increase the likelihood that there is some relevant content on your site, but it also becomes a cespool.

Rather, it makes more sense to be mindful about the instances you follow. Follow only those who are related to the content for your site. Your site should be thematic and have a vision. Follow the sites who shates a similar vision.