Why is no software so important? If you design your board well enough, you can route the programming ports somewhere you can program it in-situ, possible with other components that also need programming.

But in terms of cost, a simple microcontroller is usually cheaper than a 555 nowadays, often doesn't require external components, and so even if all you wanted was a single function like an edge-triggered pulse, or generate a single frequency, it probably still makes sense to use a microcontroller from a board design perspective. As soon as you want anything slightly more complicated, odds are you can replace a ton of other circuitry on the board with that single chip and a small program.

While it incurs a programming issue, the microcontroller will generally be more stable, less temperature sensitive, and consume less power.

For other posters saying 'just wire up a microcontroller': please self-reflect on your disregard for the concepts of simplicity & elegance. Never mind robustness, or educational aspects.

'Grab laptop, fire up IDE & plug in programmer cable' vs. 'configure the circuit using a soldering iron'. Both have their place.

I find it much easier to write a ten line program for an 8 pin CH32V003 (or ATTiny85 in past times) to do exactly the timing or SDC comparisons I want than to figure out the circuit and component values for a 555 or op-amp.

For that matter, a 16 pin CH32V003 can emulate a vast array of 7400 series devices as long as you don't need ns timing — no problem for µs. It's also cheaper.