You don't have to maintain your own fork, though. When Firefox implemented pocket, Iceweasel saw a ton of uptick involvement. I'm not sure of any popular more free to edit clones of Wikipedia though, but that is only because I have never had to seek one out. I imagine they exist. Wikimedia has not gone aginst my interests
yet - if they ever put ads on wikipedia, for example, that would be justification for forking. But that would not be your own clone, it would be a community divide. And most projects of scale realize that those kinds of forks are dangerous and act to bring the community back together by resolving a problem that is so bad it schisms the ecosystem.
This has happened before. Gnome 2 and 3 schismed, and Gnome 3 became more user friendly and configurable to bring back its users. Libva and FFMPEG split because FFMPEG was very contributor unfriendly, and then it started merging all the libva changes so contributing to libva got your changes in everywhere. Open and Libre office forked because of Oracle changes, and now Libreoffice is pretty much the only name left in town, and is more successful for it. It happens all the time in branches and private forks and message boards before it even reaches end users.
But that is the difference between MS Office and Libreoffice. When a problem is huge to the OpenOffice community, they fork and start LibreOffice, and when its substancial enough the community overrides the original developers and takes over when terrible decisions are made. If Microsoft fucks up their office (and the early ribbon was a great example of that) you are stuck, and have no power. When the version you like goes end of life, you either sit on decaying software or forfeit your preferences because Microsoft has complete control.
If Gitlab jumped the shark, you would not be spinning up your own gitlab clone to maintain yourself - the gitlab community would fork away from Gitlab Inc and create Librelab, and mindshare would drive products to it because its a seamless transition. And that is more unlikely to happen with Gitlab in the first place because the power of the user can keep the company in check from making extremely user hostile moves like Google, Microsoft, Apple, Amazon, Facebook, etc can do with impunity because users are trapped and they hold all the keys to the castle.
> Their secret sauce isn't really the software, but the service they provide.
The services are the problem. Its the same problem with Facebook - Google+ is feature equivalent, but it was dead in the water to start and its free clones like StatusNet (albeit thats more twitter) are completely dead because they aren't just personal software, they are platforms. And platforms with mindshare and the users are insurmountable.
Its not about the wiki, or issue tracker, or pages. Those are replaceable - painfully, but doable. But replacing the community of developers is not a solvable problem, because they are already on github. You have already lost. And that gives github overwhelming and dominant power in how you conduct and host free software now, with no recourse.