Regarding externalCC, it started off as a project for J-Pop fans by J-Pop fans and that has been the main audience it has been catering to up until this point. People just wanted somewhere to share translations, not really an audience to be concerned with malware/privacy since it mostly spread by word of mouth. I've heard the developer is planing on open-sourcing it for more "mature" development in the future, so let's see what will come of that.
That being said, getting people to come over to another website instead of YouTube is, as you can imagine, not something that will happen overnight (Given that you also have to consider deaf, international audiences etc. who haven't even heard of the removal yet). It's still possible to directly upload/accept from YouTube, although it's very tedious
But that probably won't last forever, I predict it will die the moment YouTube kills the old captions editor for good, which might take a few weeks seeing as the new version is kind of buggy.
In the long term I hope that externalCC and some of the other projects listed on YT Captioner's Toolkit, are integrated into open-source YouTube front-ends like Invidious. Both in terms of survivability and also easier accessibility. But that requires them to start somewhere...
And that's why I'm here to tell you about all these awesome projects, to bring you hope and to show that we can take matters into our own hands instead of whimpering about Google/YouTube's shortcomings to no avail.