I don't have an answer for this, but I know that in Poland, there are numerous engineering offices located outside of Warsaw. Engineers in these offices are paid well compared to the average Polish salary. These variations in compensation are influenced by market forces.
While engineers may be more affordable in Europe, there are trade-offs to consider. One such trade-off is the significant time zone difference between California and Europe, making synchronization challenging. Additionally, cultural synchronization can be difficult, and there is significant value in having teams that share the same figurative and literal language.