Comment by Someone

This ‘old’ equation editor is a limited version of MathType (https://en.wikipedia.org/wiki/MathType#Microsoft_Equation_Ed...) that has been supplanted by a built-in equation editor.

Chances are that Microsoft doesn’t have a license for bug fixes from Design Science (makers of MathType) anymore and isn’t willing to pay for this fix.

Alternatively, Design Science may not be able to deliver a version that, for maximum backwards compatibility, has only this fix (to minimize risks, they would have to have kept an environment around that hosts the compiler used back then)