I was recently chatting with a friend about how we used to do so much more with so few developers: 20 years ago, we developed mission critical, real time software (trading systems) in C++ with team of a couple of dozen developers. The core trading kernel team was four people. An in-house distributed process orchestration tool (both front end and back end written in C++) were two guys. I myself once managed to produce an entire post-trade risk management system for futures contracts in a couple of months, working alone. Today, I see teams of 60-80 working on web and mobile applications where the vast majority of operations are CRUD, with some transaction/queue complexity at the extremities.
I think the difference is tech churn. Back then, what few dependencies we had in terms of either runtime libraries or development time tools, were stable: the standard library, compiler, unix commands and bash scripts, and some internal libraries. Much of our time and focus went into figuring out the right algorithms and data structures, with coding coming in second. Very little time was spent on selecting, configuring, updating, rearchitecting or replacing tech stacks and tools.