Serious professionals use one or more spending models to determine budget.

My favorite is the Gordon-Loeb model[0], but there are others that are simpler and some that are more complex. Almost none that imply the budget should naively grow in lockstep with prevelence linearly.

I think TFA doesnt really mean to imply that it should, merely that there is a likley mismatch.

[0] https://en.wikipedia.org/wiki/Gordon%E2%80%93Loeb_model