Hopefully this eliminates any doubt on Gab's real mission. It isn't free speech.
It may seem juvenile, but it is the kind of thing people do in an adversarial situation when they have no better hand to play, AKA they "got nothin'".
I have no idea why they did it in this case, but I've seen it done to stop overly aggressive antivirus or antispam software from looking inside when the archive contains stuff likely to trigger false positives.
It's because they are juvenile, far-right goons.
Naturally, most of these majority belief systems and viewpoints aren't functionally being suppressed, because many employees at these companies hold the same views. It's usually just the extremist stuff, and some of the people who bail from Twitter to head to Gab or Parler end up causing trouble there too by being so extreme they run afoul of those sites' incredibly lax and generous policies.
I could understand this complaint if the government was applying force or other punishments (financial penalties, etc) to suppress a majority viewpoint, but in this case it's private corporations exercising their rights to exclude majority speech from their platform. This is an important right for them to have regardless of how popular a view is.
It wasn't that long ago that polling numbers showed the average American supported the Kent State massacre, and it wasn't that long ago that interracial marriage was illegal in parts of the US. The nature of "majority views" and the impact of reducing their visibility is difficult to grapple with.