Why the dichotomy of “small” and “large” scale dev dev?

And why do I rarely seen any context of transition states between the two? For instance: When does a small-scale but growing app no longer qualify as "small", and does it make it automatically large-scale at that point? (maybe it's similar to the heap paradox?) Another sample topic: Companies that prefer to hire for experience in large-scale web dev. Small-scale devs want to learn but lack the means in their current job. And they do not know whether the best approach for their software is a gradual change or you turn it on like a light switch.

Providing more context in when and how small turns into big could be especially useful for professionals who only know small-scale dev practices but are trying to bridge the gap.