I’m a structural engineer, running nonlinear analyses of buildings. These take about 3-5 days to run on an i9-9900k. The program runs each earthquake simulation on a single core.

An audio processing chain is necessarily single-threaded. e.g. if you want to simulate a guitar rack you have to first simulate the distortion pedal before the amp, the amp before the cab, the cab before the delay / reverb / whatever 200 other effects you're chaining. And you have to do all that in tight deadlines, e.g. <= 2 milliseconds.