I used to work on these problems in school all the time, but once I decided to join industry I encountered a bunch of these Lisp-style engineers who love computation in the abstract but not the application thereof. Scala seemed to attract a lot of folks like this. Maybe if I had gone into scientific computing I would have found more.
I get to use these skills every so often though. When I was designing one of our early two-level caches at $WORK, I wrote an analysis of chosen TTLs and jitter values by looking at microservice latency distributions. I've debugged a nasty concurrency issue by modeling it in TLA+ and then fixing the bug (full disclosure: once I thought through the TLA+ model, the bug was fairly obvious to me, but the modelling itself was the valuable exercise.) I've used MILP solvers for capacity planning our boxes. I've designed queue backpressure through probabilistic analysing. Each of these things has been crucial in designs I've used, but I only encounter a problem like this once every some years. (And these days I often write more docs than code.)
I quite frequently encounter code that can be made much faster (at no significant loss of value generated) by sampling or using other statistical techniques to reduce precision.
Also flows and buffers in the software that can be improved with queueing theory. Logic that can be simplified with boolean algebra.
I get to use these skills every so often though. When I was designing one of our early two-level caches at $WORK, I wrote an analysis of chosen TTLs and jitter values by looking at microservice latency distributions. I've debugged a nasty concurrency issue by modeling it in TLA+ and then fixing the bug (full disclosure: once I thought through the TLA+ model, the bug was fairly obvious to me, but the modelling itself was the valuable exercise.) I've used MILP solvers for capacity planning our boxes. I've designed queue backpressure through probabilistic analysing. Each of these things has been crucial in designs I've used, but I only encounter a problem like this once every some years. (And these days I often write more docs than code.)