I've been freelancing for quite a while and I think you can find some projects that you can do in C++. I don't think it's easy to find remote work in, specifically, C++ for several reasons:
1 - Companies want cheap productivity developers (yeah :S), it's very common that they force you to use some hype productive new framework/language regardless of what you think about it.
2 - If a company is going to invest in system level development, it's very hard to find another new decent C++ remote programmer. This is a very critical point. If you fire a javascript/python developer you can find another on in a matter of hours.
3 - If a company needs stuff in C++, probably the company is scaling and needs to recode some components. Usually they have the budget to hire decent C++ developers non remote.
4 - Myths like "C++ is for genius", "You can't be productive in C++", etc.
5 - C++ is not trending these days and it impacts the hiring and/or project stack decisions.
6 - Most remote projects are easy shit, you'll be amazed by the quality of projects and, sometimes, the freelancers hired themselves. Most of the time the projects don't need a fast runtime but new managers.
7 - Agile methodology is often used as an excuse to change the requirements every 2 weeks or so, it's not rare to find such management. You need to have the right tools and community to survive such environments. C++ was my 3rd language but I never used it during freelancing/remote work. Today I feel very comfortable using node because I know this kind of stuff happens, and when it does, it's much better to have things like NPM and a big community just to remain sane and keep up with deadlines.
Keep in my that these "reasons" are based on my personal experience as a freelancer. It's possible to find some remote work for C++ but you'll find to try much harder than, for example,a node/python developer. Try to focus on areas where C++ is critical. If you contribute to well know C++ open source projects, it's just a matter of time to get noticed and hired remotely.