Russian Trucks and Cars

[Eduard Sorokin]

This is very large and difficult question.
The main version of answer - Soviet designers were aimed to provide mainly the National Defence with their vehicles. It is known, that all vehicles (or their most part) in any country are the "military reserve", and this reserve could to be impressed in military use in any moment.
It is not very important, how looks the military truck - this truck must to be hard, cheap, powerful and reliable only. It's appearance is not main subject.

Due these reasons, Soviet designers did not care about civilian customers, and designed those almost similar vehicles.

There were many experimental designs with different appearance in the USSR, of course. However, these designs were abandoned, or not adopted, or cancelled in favour of more simple, cheaper, or "easier-in-production" types.