Probably wasn’t about aesthetics, probably all he had. My guess, the original willys backend was probably rusted out or damaged, and probably didn’t have a Moskovich Poebda to scrounge parts from, but did have a dead lada, or at least part of one.
Soviet citizens often built vehicles out of scrap, considering the high cost, and years-long waiting lists for new Soviet cars. I wouldn’t have been surprised if a soviet man called his union rep to clear him for a new 1971 vaz 2101 , and was still waiting for it in 1979! Often easier and cheaper to build it yourself.