<p>Math majors are highly valued not because what they learn in school is incredibly useful, but because what they learn in school is incredibly difficult. A graduate prep. program in mathematics is probably the most difficult major out there. A student smart enough to do well in such a program is probably smart enough to do well in any intellectual field.</p>
<p>It probably is the case that they do not know enough about engineering to get engineering jobs straight out of undergraduate school. However, math majors are probably looked upon quite well by graduate engineering programs (note: I may be making this up, but it does sound reasonable to me), and could get engineering jobs after receiving a graduate degree.</p>