Because if, as the regulator, you fail to benchmark what they gained then your laws can be ignored and your fines paid as simply a cost of doing business.
Its why you find the Australian regulator for consumer affairs handing out $200m+ fines to telecommunications companies, for example.
By that logic regulators should lower fines if the action wasn’t profitable. Which creates an expensive legal fight around the net profits of some action were after guilt is determined.
Instead, it’s much better to scale fines based on the scale of the entity involved, which also results in huge fines, but it’s easier to measure revenue. Thus the fines are more broadly effective, and you can still escalate if they don’t stop.
Like in Finland where speeding ticket fines are based on your income. For instance, in one well known case a businessman was fined €121,000 for going 82 km/h in a 50 km/h zone.
That's considerably more than someone near me who was doing 245km/h in a 90 zone (Well 55mph which is 89km/h). I still don't know why that person didn't lose their license (other than the obvious fact that they were rich enough to afford the Lamborghini that they were driving in); it wasn't just any 55 zone, it was one with a reputation for being dangerous.
And before anyone calls this crazy, note that jail time costs you your time, whatever that's worth. This is the same idea without the physical incarceration.