What region are you in, and what instances are you failing to access? Smaller/newer instances generally don't have a lot of "peer instances" seeding their content, so that could be why you're having trouble accessing it.

Not everyone has Youtube-level bandwidth, but even Youtube is very hard to access in many parts of the world. Peertube is designed in a decentralized manner so that people who enjoy your content can setup a local instance in their neighborhood to mirror (seed) your content.