Isn't math necessary for most real-world engineering, and even in CS research? And what were you expecting? You asked for a cutting edge Bell-Labs type of R&D place, and that's what research is all about, even in CS.

You'll work with a lot of new yet-unproven theoretical concepts for which you need a lot of math to prove they have a high chance of working in practice and being better than existing solutions, before someone approves budget for the costly development and implementation of an actual product.

In the case of mechanical engineers, maybe 1 in 50 bonafide geniuses in mechanical engineering are also simultaneously math geniuses. Just my personal hunch.

There's really not that many positions, so it's unrealistic to expect recruiting standards to be much lower.