Probably because it's so useful in detecting the "smell" of fraudulent numbers. Fraud is, of course, going to be most common where money is involved, but it can show up in many other places: for example, someone might be tempted to fudge their scientific data if their career depends on getting numbers that aren't quite where they want the numbers to be...

If a number distribution that should be following Benford's Law isn't, that's nowhere close to actual proof of fraud, but it can be a pointer helping you know where to start looking. Because if all the files except this one have numbers that follow Benford's Law, yet this one doesn't, then that's the place where you start digging for other, more positive, evidence of manipulation.