the correct way to control randomness in scientific code is to have the RNG be seeded with a flag and have the result check out with a snapshot value. Almost no one does this, but that doesn't mean it shouldn't be done.
Contra your assertion, many people do some sort of regression testing like this but it's isn't terribly useful for verification or validation - but it is good at catching bad patches.
I used to be a scientist. I get it, getting scientists to do this is like pulling teeth, but it's the least you could do to give other people confidence in your results.
Ok, that's a reasonable ask :) But yeah as you implied, good luck getting the average scientist, who in the best case begrudgingly uses version control, to care enough to do this.