It's C notation. Other languages use other notations like ~= or /= or <>. And any conceptual overloading of ≠ is a tiny fraction of the problem with = (it's too bad ASCII'67 dropped the ASCII'63 ← in favor of _).
But, taking your point, a ligature ≠ would be overloaded in representing != and ~= and /= and <> and becomes potentially very risky.
And if you go a bit beyond top 20, there's Haskell: /=