Because small programs are really quick and easy to write, there was never a bottleneck making them and the demand for people to write small programs is very small.
The difficulty of writing a program scales super linearly with size, an experienced programmer in his current environment easily writes a 500 line program in a day, but writing 500 meaningful lines to an existing 100k line codebase in a day is not easy at all. So almost all developer time in the world is spent making large programs, small programs is a drop in an ocean and automating that doesn't make a big difference overall.
Small programs can help you a lot, but that doesn't replace programmers since almost no programmers are hired to write small programs, instead automatically making such small programs mostly helps replace other tasks like regular white collar workers etc whose jobs are now easier to automate.