The purpose of computers is to perform calculations. Then we built a massive pile of abstractions on top of that souped-up calculator to make it into a general purpose machine. Then we built a small calculator app on top of those abstractions. A lot of work to get back to square one.
(This obviously misses the point that we made computers usable by mostly anybody along the way, but it’s still funny)
As someone who sat alongside when my granddad soldered 8080 clone to the board, entered commands via switches, and seen binary results on a LED display (not a modern LED display, but literally a row of 8 red Light Emitting Diodes, you know) I tell you with a great confidence that clacking 1+2x3 on a keyboard and seeing an answer on SVGA+ screen is much quicker and more convenient than:
- planning a program
- implementing missing mul and/or shl instructions in your mind
- managing register pressure for more complex expressions
- having to start from scratch on a mistake
- debugging with a multimeter
Even if you think of MBR-style calculator, there is at least dozen kb BIOS and dozen kb VGA BIOS to start with a blank screen that can do cursor and digits. There is nothing cheap or straightforward down there, and the first thing people did was abstracting baremetal away ASAFP.
One way of thinking of it is that a physical calculator has two parts - the circuitry that performs the calculations and the UI - in the form of physical buttons, displays, and the connections between them and the calculation circuitry - that allows people to effectively make use of it for their calculating needs.
A modern CPU has got the calculation part covered by itself, but it still needs the UI. Of course there are other kinds of UI for people to do calculations - for example Excel, or programming language REPLs - but desk calculators had pretty good UI for some use cases, so it makes sense to have an option based on them.
That only seems to explain why it could seem odd to buy an entire desktop PC to only ever use it as a basic calculator. In that case, it might make more sense to just buy a calculator. But there's certainly nothing odd about buying a general purpose computer and then use it for lots of different specific purposes, one of which is numerical calculation.
(This obviously misses the point that we made computers usable by mostly anybody along the way, but it’s still funny)