Too many years of inadequate display technologies (text only) plus some powerful notations which could describe math to computers in other ways (using functions like sqrt() and pow()). Also mathematicians like to invent typographically hard to use symbols, which would need to be widely implemented first before they can publish their research, so programmers only make specialised packages for mathematicians instead of system-wide support.

The notation is far too complex and ambiguous, with too much reuse of notation to mean different things in different subfields. For example, superscript numbers are used for exponents, and subscripts are for indices, right? Well except for certain cases where vectors are indexed by superscripted numbers instead.

Mathematicians should have been taught to use Scheme syntax instead.

Because Don Knuth only invented digital typesetting he had time to only write TeX and Metafont.

Had he also done the same for display managers, we would be fine.