Calculators do not implement “what conventions are typically used in practice.” Entering symbols one by one into a calculator is a fundamentally different process from writing them in a sentence. A basic traditional calculator will evaluate each step as you enter it, so e.g. writing 1 + 2 * 3 will print 1, then 3, then 6. It only gets one digit at a time, so it has no choice. But also, this lends itself to iterative calculation, which is inherently ordered. People using calculators get used to this order of operations specifically while using calculators, and now even some of the fancy ones that evaluate expressions use it. Others switched to the conventional order of operations.