C++ and even more so C are programming languages which require the programmer to manage memory resources (although newer versions have introduced features that automate much of it). Doing this incorrectly can introduce vulnerabilities that allow an attacker to access data that they're not supposed to. Rust and Go are newer languages that are designed to mitigate this danger. The Linux Kernel is perhaps the most influential software project still being written entirely in C.

As for why the White House has something to say about it, I got no idea. I would have assumed this would be under the purview of NIST or something.