1. With everything being so mega-project and planned-ahead nowadays, you rarely need that "oh lemme just calculate it for you right now" on-the-stop calculating. If a piece of work needs that, in my eyes somebody has already failed upstream.
2. For simple calculations, a normal computer will work fine (and you're likely using one anyway in jobs that need calculating).
3. For complex calculations, you will likely be writing a script in some programming language in order for the calculation to be easily repeatable, etc.
I can just imagine there are loads of people in jobs that do need real physical hand-held calculators every day, and are shaking their fist at me right now :P