> If use of C++ declines then I don't understand how that would make the language a lesser tool.
The hypothesis is that C++ will decline because it becomes the lesser tool (where "lesser tool" means it excels only in increasingly small niches) if it doesn't adapt. That said, the C++ community seems to want to adapt and remain relevant, as indicated by its significant progress over the last decade.
As for why someone might care about the usage of a programming language: because "ease of finding developers" and "quality and breadth of ecosystem" are major factors in deciding on new projects. I.e., "the best tool for the job" is often the one with the broader ecosystem and more developers, all else equal. So these factors feed back on each other.
The hypothesis is that C++ will decline because it becomes the lesser tool (where "lesser tool" means it excels only in increasingly small niches) if it doesn't adapt. That said, the C++ community seems to want to adapt and remain relevant, as indicated by its significant progress over the last decade.
As for why someone might care about the usage of a programming language: because "ease of finding developers" and "quality and breadth of ecosystem" are major factors in deciding on new projects. I.e., "the best tool for the job" is often the one with the broader ecosystem and more developers, all else equal. So these factors feed back on each other.