I did work for a while in/with a small hardware company, and basically how we did things was we integrated a complex off-the shelf CPU board, to a custom 'host' board that housed application specific logic.
Signals integrity analysis used for integrating DRAM is a difficult skillset, requires trial and error, and if you manage all the design complexity somehow, manufacturing is likewise difficult. If you show up with a 8 layer PCB littered with BGA components, most manufacturers won't talk to you if you don't have volume or aren't willing to pay astronomical prices.
And let's not get into wireless - antenna design and interference testing is its own dark art, and even if you manage to make something that works, you have to certify it in every single country/economic block you want to sell to.
And all this to supplant a ready-made Pi Zero or ESP board. that costs basically nothing.
Clearly much bigger shops than ours have realized this - there are many high-volume commerical products that use a Raspberry PI as brains, or smart speakers using ESP32.
I assume your application host board wasn't two LEDs and a button. Using a module is one thing, using essentially only a module is another.
My point is, laying out very simple hobbyist-level designs is not 99% of PCB design effort in the world (the original claim).
It's not "envelope-pushing crazy designs" (per the original) to have 500 or 1000 or more components on your board even if you do use a module to offload the CPU and radio (or the field bus in industrial contexts). That's just normal levels of complexity.
And even if you do make a boutique smart speaker with a module and can afford it because it's a high-end device with margins, if you get to real volume, saving a dollar a unit by integrating might be worth it: you can still see change of out the savings after getting a design consultancy to redo your board if you're shipping millions of units.
Signals integrity analysis used for integrating DRAM is a difficult skillset, requires trial and error, and if you manage all the design complexity somehow, manufacturing is likewise difficult. If you show up with a 8 layer PCB littered with BGA components, most manufacturers won't talk to you if you don't have volume or aren't willing to pay astronomical prices.
And let's not get into wireless - antenna design and interference testing is its own dark art, and even if you manage to make something that works, you have to certify it in every single country/economic block you want to sell to.
And all this to supplant a ready-made Pi Zero or ESP board. that costs basically nothing.
Clearly much bigger shops than ours have realized this - there are many high-volume commerical products that use a Raspberry PI as brains, or smart speakers using ESP32.