There was a very good reasons for it, indigenous designs were obsolete by the time they left the drawing boards and countless design bureaus cost stupid amounts of money while producing dozens of incompatible computers. By the time they decided to adopt ES EVM they lagged by some 5 years and continued to lag further behind.

Conversely, the Soviet Union took the PDP-11 ISA to its limits... including home computers with framebuffers and programmable calculators.