A few issues I’ve seen with adoption in the federated/open source world-

There is a technical barrier to entry. The fact that you’re on a website that’s connected to other different websites in the same interface is one that people aren’t particularly familiar with. For a social website, questions around moderation and who you’re interacting with are problems which are hard to address if you’re unwilling or incapable of learning the terminology you need to learn to understand how this works.

Each entry point into this website system is slightly different as well - how it presents itself, the design, who participates on that entry point, what kind of discussions exist. You might stumble across a lemmy instance as your first introduction to lemmy that doesn’t appeal to you and not recognize that it’s not everything that’s available on lemmy and discovering that can be difficult. The same is true of other federated websites.

As you mentioned there’s also issues with algorithmic feed. This is what leads a lot of people to stick with a particular platform. They want content to come to them, rather than searching for it, and they aren’t always aware what content they want. Federated content is much more pull oriented than push oriented and until someone codes an algorithm to push I think there will be a lot of resistance with a particular subset of individuals who are interested in pushed content rather than pulled