https://en.wikipedia.org/wiki/Experience_curve_effects
During WWII, it was observed that each doubling of output reduced labour costs (or increased labour efficiency) by 20%.
Moore's law is dependent on the density of transitors (the count doubles for a given cost every two years). Increased density => increased computing power and efficiency, and speed.
Chip design is dependent on numerous factors: die size (e.g., 14 vs. 9nm photolithography dies), silicon purity, fab cleanliness (much as with cascade refrigeration, chip fabs now have multiple concentric zones of increased cleanliness), and the power and capacity of the software that's used in chip modelling itself.
The law is also not entirely exogenous as it relies on market forces and demand: need for increased computing power tends to proceed at a predictable rate, and the ability to make use of more capacity is also constrained by existing practices, software, programmer skill, etc.
Then there are the other non-CPU bottlenecks. Disk and memory have long been the foundations of that, increasingly it's networking. The tendency of old technology and layers not to die but to be buried in ever deeper levels of encapsulation means that efficiencies which might be gained aren't due to multiple transitions and translations -- the reason why a 1980 CPM or Apple II system had a faster response than today's digital wireless Bluetooth keyboards talking to a rendered graphical display. Bufferbloat, at the network stack, is another example.
But: the main driver for Moore's law is increased density leading to increased efficiency (the same centralising tendency present in virtually all networks), bound and limited by the ability to get power in and heat out (Amdahl's observation that all problems ultimately break down to plumbing).
The transistor can only get so small before it stops working. There are many issues with required extreme ultraviolet light sources (lasers) and allowed amount of impurities in silicon waffer. And R&D cost for each iteration of lithography is getting higher while bringing less benefits.