I strongly doubt that C++ is what's standing in the way of Ada being popular.
Ada used to be mandated in the US defense industry, but lots of developers and companies preferred C++ and other languages, and for a variety of reasons, the mandate ended, and Ada faded from the spotlight.
alt Hacker News
Ada used to be mandated in the US defense industry, but lots of developers and companies preferred C++ and other languages, and for a variety of reasons, the mandate ended, and Ada faded from the spotlight.