Is that the same reason for why they keep Lenin mummified in a mausoleum? 
(I was under the impression that the erased people were executed)
Often they were people who were executed, but sometimes they were just people who shouldn’t have been in the shot, or who had a disapproving expression, or whatever. There are lots of reasons to doctor a photo. One of the photos in that collection shows a man who was airbrushed out because it looked like he was showing Stalin which direction to go in, and that was deemed impertinent or something. There’s another one where some signs were airbrushed out and their slogans replaced. There was nothing wrong with the old ones - one was a plain shop sign, and the other a standard communist flag. But I guess someone felt like they just weren’t powerful enough.
That site is a treasure trove of photographs, I must say. I just spent the last hour clicking through some of the other photo galleries. Some of them are incredibly depressing. For example, the beaches of St. Petersberg. Almost all the trash on those beaches is recent. People just dump their garbage everywhere. I guess that’s a symptom of the breakdown of civil society. No one cares…
In general, many of the galleries of modern Russia depict a nation decaying at a rapid rate. When the state is responsible for everything, and then the state vanishes, then no one is responsible. Without property ownership, major buildings and infrastructure are just left to rot away… You can see the same thing in Detroit today. Very sad.
It also makes you understand why, even though the Soviet Union was a horror, many Russians still feel nostalgic towards it and some even want to go back to those days.