Like everything else Soviet, there is no certain information on the origins and the reason behind the specific design of it, but the difference between the kurtka and the gi, used in BJJ and judo, is actually quite great.
Based on several different types of folk style wrestling, the kurtka includes the most common features of their uniforms.
First, the kurtka has belt loops, making it almost impossible for the belt to fall during a fight.
As a result, sambo has a lot of belt grip strategies, since in standing an in parter, you always know the exact position of the opponent’s belt.
Second, the kurtka has epaulettes.
This is most probably a Caucas mountain influence, where the majority of the national costumes of the region are featuring epaulettes.
Of course, this small detail also brings another option to the already complicated, sambo grip fight. One side grips, cross grips an etc, all could be executed from epaulette, firm grip, making the life difficult for any opponent, not used to the traditional sambo grips.
On top of that, the kurtka cut is usually tight, making it hard to grip and easy to break grips.
Sambists often compensate with superior strength and endurance training, making for their image of hard nosed and not really desired opponents in MMA matches.