If you read the Stepper code for Marlin @ https://github.com/MarlinFirmware/Marlin/blob/1.1.x/Marlin/s... you will see it's nontrivial... bunch of PhDs implementing nontrivial maths in a highly constrained environment. That's cute but not demonstrative of real world concerns. In such cases, you would absolutely throw more hardware at the problem, eg. for motion systems maybe dedicating one 'dumb' MCU per axis and outsourcing planning to a more rational/powerful environment.

That automatically means you have to be shipping at least 120K units just to break even with those costs. But you are also getting to market 3 months later which itself has huge business costs which means you probably need to be shipping 200K or more units. That's a pretty big number for a lot of embedded device designers.

If you double your chip constraint from $0.13 to $0.26, then that same team must now ship a million devices to break even.

It's a buck and change on those--same as ARM Cortex M series.

For anything commercial? Almost certainly not.

For one-off makers/non-engineers? Maybe. The Arduino ecosystem is really hard to beat for non-programmers.

Same for many of these devices. Mature libraries, low cost, ease of use all play a part.

Alone, it's the sort of thing you might use for a kid's toy that you hope to make into the next big must-have Christmas hit. You'd need to make millions upon millions of them, and maybe $49.95 is your target price.