Because the only place you really need them is in mathematical/scientific computing, and while many scientists tend to pick up a little programming for their research, the vast majority of computer scientists and programmers, in particular the ones with the interest and ability to work on languages, are not concerned with mathematical modeling/processing. It is a fairly rare interdisciplinary combination.
Plenty of DSA work has more optimal representation and evaluation as matrix arithmetic. Particularly graph traversals and transforms which are heavily used in optimizing compilers.
