As merely an (irregular) user, package fragmentation can make it confusing to search for packages. My suspicion is that the overall ecosystem could be healthier overall (=larger bus factor) if there were stronger tendencies to merge efforts instead of creating separate packages.
However, given that Julia and its ecosystem are quite “academic-affiliated” in nature, I suspect the incentives are a little aligned against that – I think it’s easier to get published when creating your own separate package than for “look, I made a series of big PRs against otherpackage”. 
One example that I recently encountered was that I stumbled upon GitHub - SciML/GlobalSensitivity.jl: Robust, Fast, and Parallel Global Sensitivity Analysis (GSA) in Julia. It uses the “GSA” in its Readme, which I assumed to stand for “Global Sensitivity Analysis”.
Getting curious about the package name, and searching, I found GitHub - lrennels/GlobalSensitivityAnalysis.jl: Julia implementations of global sensitivity analysis methods., so that seems to have occupied a clearer package name already, so from here it looks like the GlobalSensitivity.jl authors were probably aware of the other package. GlobalSensitivityAnalysis.jl exists for one year longer, and has a similar amount of commits and activity. I’m wondered why a separate package was created, instead of pooling efforts.
From skimming the docs, it seems the SciML one has more methods implemented. No indication why those could not have been added as PRs to the already existing packages. I could not find any indication of an effort to join forces. The SciML one has a published paper, but its “Statement of Need” does not mention the existence of the other package.
At this point I deferred a deeper trade-off analysis until I really needed such a package. I walked away wondering if the maintenance situation (in the always maintainer-strapped OSS world) would not be better if people were joining efforts more (so yeah, this topic). If there were gentle incentives from the ecosystem/culture towards that, I guess this would not be a bad thing.
But then, the real world is complicated and full of humans. From another ecosystem and software area that is littered with small and subsequently abandoned projects, I already know that achieved de-fragmentation is a very hard thing. Maybe getting critical mass orgs (=>SciML?) and ending up dominating is the most promising avenue?