When I first joined the server in mid-March of this year, this server was in 1.9 and didn't have as many hackers. At least this was my case (not sure if others had the same experience) since I didn't have any experience with hackers when I played my first 1.9 SG game shortly after 1.9 release.
In list form (my theory):
-For sure, it's because it took at least over a month after 1.9's release for hacker developers to code all the hacks for 1.9. Pretty sure the toughest nut to crack was kill aura since all other hacks are almost the same.
-It was around August of this year that more hackers came since the 2nd, ineffective, punishment system came out.
-This also pardoned ALL offenses rulebreakers previously committed, giving them an easy 2nd chance of hacking on the server again. (Thanks,
@Chimp for reminding me of that)
-Beta anticheat drew more hackers to this server.
-Mineplex used to be a hacker-infested server. It still is, but not as much or shouldn't be ever since GWEN came out. I have no clue about this since I left Mineplex in June.
-It's the 3rd biggest (or on par with Mineplex during certain times of the day). Naturally, more players means more hackers.
-The majority of the playerbase are very young. Based on observations in real life and online, most of the time kids will test the limits by breaking the rules.
-Some YouTubers such as xTurtle promote hacks in their videos by hacking on servers.
-As an example of how YouTubers promote servers, let's look at TCR (TheCampingRusher) and 2b2t. Prior to June, 2b2t had <100 people on. When TCR promoted 2b2t, a lot of players came to 2b2t, filling its queue to over a thousand players during the summer. Why? YouTubers act as a way to promote the server. It's money for the YouTuber and it's money for the server because of more players.
I'm not sure what Cube was like before 2016. Was it a small(er) server back then?
EDIT: In retrospect, when I used to play Mineplex a lot last year, a lot of hackers were on the server. I'll assume it's natural for a server with a weak anticheat to attract hackers until it's resolved. The same thing happened over there - many hackers, including donors, hacked in every single game. Many players had their stats ruined and many games became unplayable, if at all.