Over the last decade we have started to approach the size limits of silicon semiconductors. So simply making transistors smaller and adding more of them became more and more difficult and expensive. We have also reached the practicall limits for cpu frequency in silicon.

Then there is architecture limitations, x86 is a rather bad architecture for a modern cpu, and while arm is better it also somewhat suffers from the fact it was made in the 90s. RISC-V hives hopes of improvement on this front tho.

So to get back to the growth speed of the second half of the 20th century we will have to develop new materials for semiconductors or alternative methods for computer construction.