Yes, 45k USD remote for US companies, as opposed to entry level salary for MSc grads of 18k for the field I'm working in, in Chile. As I said, that's the lowest salary offer of remote jobs. The theory is numerical analysis of partial differential equations, specifically, the finite element method (for CFD, fluid-structure interaction, thin shell mechanics, buckling, and so on). To have a basic understanding of how to code custom FEM programs one needs at least an understanding of the fundamentals of functional analysis + analysis of PDEs + tensor calculus + the specific theory of physical application involved. These are non-trivial skills that take years and years to develop, so I would advise to anyone interested that it's best to get a job as a dev instead. I do it out of passion and because my family has a history of civil/mech eng.

The reason for such spread, I suspect, is that there is not much market for FEM professionals outside of the US and Europe, and if it exists, it's very small and unsophisticated.