Why do some computer keyboards have a "NUM LOCK" Key?

My research into this indicates that before the invention of arrow keys the NUM LOCK key converted some of the number keys into arrow keys. That’s cool, but Dell and some other computer keyboards like HP are still being made with arrow and NUM LOCK keys. This presents me with a slight irritation. I frequently (by accident) hit the NUM LOCK key while typing in the numbers pad at work causing me to waste time by redoing my work. I was thinking about super gluing the NUM LOCK key in the up position but everyone would know that I did it. So why are NUM LOCK keys still on some of the latest computer keyboards?