Calculators are more complicated than that. Some have CAS (Computer Algebra System features - like factoring polynomials) and these features have to be disabled for some standardized tests. So, for the homework, you can 'run what you brung' but when you take the tests, you have to do without. The HP48GX can probably run as-is for these tests and it's better the devil you know.
I've mentioned (too many times) that I am helping my grandson with Calc I. We have the bar in the kitchen set up as a "homework station". A pair of 27" monitors, two Surface pads, a color laserjet, 2 HP48GXs and a bunch of quadrille paper (engineers draw pictures!). The calculators get the most work when we're dealing with numeric problems. Trig and some word problems tend to be numeric. Limits? Not so much... There is simply no way we would want to do without the HP48GXs. And the TI nspire and the HP Prime are sitting on the counter, unused!
The touch and feel of a real calculator far surpasses the emulations. Tactile response, button sizes, hand motion, all of the ergo things favor the real calculator.
Now, when it's time to see how to solve a problem, we head over to symbolab.com. If we just want to see a quick graph, it's off to desmos.com. Maybe a Khan Academy video... That's the reason there are two tablets and displays. We're working here, not just fooling around! Homework runs around 70-80 problems per week and we spend on the order of 15 hours per week working them. Sometimes more, sometimes less but, still, a lot of time!