The main thing that has changed over the years is that the software stack has grown deeper, and today there are many more people working at higher abstraction levels where a lot is handled for them.
But under the covers, little has changed. Someone must write and understand code all the way down to the hardware. You can bet that people writing kernels and drivers think a lot about space and speed. Or write some code for one of the low cost micro-controllers that are in virtually all electronic devices and you won't have the luxury of a large software stack.
There are very likely *more* people writing low level code today than 20 years ago. Only the percentage of programmers writing low level code is declining because there are many orders of magnitude more programmers writing higher level code.
Make it right before you make it faster.