In the chart above, there is a break point in mid of September. I think that it makes lot of sense.
After the demotion implemented, there were massive merit abusements in the forum, lots of Junior Members demoted got promoted again due to merit abusements.
Personally, there is a hypothesis that massive newbies got their first merits due to merit abusements after Sep. 2018, or due to their successfully pseudo-quality posts.
Eventually, most of them got banned.
The chart probably presents wrong x-axis scale, you stated there are 1934 newbies got banned, but the chart shows nearly 10k newbies got banned.
You should clarify it a little bit if the chart is right, or should correct it if it is wrong.