No, it would not be more popular if there was one distro. That wouldn’t solve any problems.
This is a fundamental misunderstanding I see among many people, especially those outside/new to the Linux world. They talk about having too many choices where it’s overwhelming to pick from. But it’s not like ice cream flavors where “Oh I like chocolate and vanilla and strawberry? How can I choose?” where some people can get choice anxiety; if you think that’s comparable you just don’t know about how Linux fragmentation works.
Now, that’s fine; not everyone will know everything, and this concept is not always obvious to everyone. That said, an argument made from ignorance is not a valid argument.
Let me explain why fragmentation doesn’t work this way.
In every piece of software that is fragmented in the Linux world, it’s not arbitrary. It’s not people making hundreds of different things “just because.” There’s always a correct choice for each person. Different tools in the same area to suit different needs. No, not all tools are on equal footing lacking unity. They all benefit from the same standards but implement the features that matter to that tool. Unifying them solves nothing. We may not even get a tool out of it as people would fight over the directions of the projects.
For instance, why are there different DEs and WMs? Because not every DE has the workflow a person wants. I can’t stand the Windows way of UX; I think it’s terrible. If there was only one distro, and it came with KDE, I’d be very frustrated as there’s no good tiling options!
The different distros are not ice cream flavors; they exist to fulfill specific needs. You pick your distro, DE, etc to suit the way you want to use your computer. Everyone has a way they want their computer to work whether they realize it or not, even if that way is just how Windows does it.
There’s not an overwhelming amount of distros; that’s a view stemming from a lack of understanding. Fragmentation is not a problem.
then that distro would probably be better than Windows and more people would move to Linux
So as you can see, this wouldn’t be the case. That distro wouldn’t serve people’s needs, just like Windows doesn’t serve people’s needs.
The problem with Linux is not its fragmentation - that’s it’s superpower; there are distros that will meet the needs of everyone already. You just have to figure out what you want from a computer. If it’s just how Windows does things then, well, there are DEs and distros out there already made to function like Windows! Give Mint a try, for instance.
The reason Linux isn’t more popular has nothing to do with not having a good-enough distro that can beat Windows. What that looks like is different for different people, and I guarantee all of them exist somewhere.
Tbh Linux already is better than Windows (and Mac) on every front except two:
Lack of industry-standard software for certain fields as well as a handful of specific games
Normies will use whatever their PC comes with and will be too scared to reinstall, and Windows and Mac come on almost all devices by default.
P.S.
similarly to how most of us use the same kernel
This isn’t the case. We don’t even use the same kernels!
First, many distros use very different versions and second, some come with kernels that have major tweaks and customizations.
Not to mention the various modules and kernel parameters that get enabled and added.
There are plenty of kernel tweaks.
EDIT: I like what another user said - “Linux is modular, not fragmented.”