During his postdoc, Gariépy's had one second-author publication in Nature Neuroscience[4], which probably wasn't enough to get a tenure-track professorship. If, like the first author on that paper, he had gotten an assistant professorship at a prestigious university[5], he probably wouldn't be airing his dirty laundry. Also note that he is a YouTuber[6] and has a book coming out according to his Twitter profile[7], so he's probably trying to leverage any notoriety he gets from ragequitting his postdoc to jumpstart his career in science journalism.
0: http://today.duke.edu/node/132805
1: https://www.linkedin.com/in/jeanfrancoisgariepy
2: https://www.bostonglobe.com/metro/2014/10/04/glut-postdoc-re...
3: https://www.bostonglobe.com/business/2015/09/02/cambridge-pl...
4: http://www.nature.com/neuro/journal/v16/n2/abs/nn.3287.html
5: https://medicine.yale.edu/neuroscience/people/steve_chang.pr...