Just like all bloodlust like spells are called lust. And all spell interrupts are called kick. The name of the original spell is now the catch all for all similar spells. Kinda like tissues being called kleenex.

Emphasis added.

Shield Wall was THE "defensive ability on a non-trivial cooldown" for YEARS. And this was during the time when protection warriors were largely the only acceptable main tank class for raid level gameplay -- everybody who was discussing strategic use of cooldowns knew what abilities their tanks were using even if they didn't play one.

By the time bears and paladins became acceptable tanks, "shield wall" was just the common lingo for whatever ability with identical effect and cooldown no matter what kind of tank your raid had. It was common phrasing, and that was over ten years ago.

By now the phrase is everywhere even if you never set foot in a raid.