A lot of people who go to other countries to teach do so for the experience of embracing another culture and society when they are young enough to actually appreciate the experience. You mention Teacher Luke (or people like him) who ridicule the culture they teach in, but I'd suggest another possibility for why people like him do that: It may have more to do with coming to that foreign country to embrace this new culture, but the people of that culture cut him off completely, so he ends up doing what most young people do: He stereotypes the culture he's experiencing because they're not actually giving him a chance to explore the real thing. So, where you see normality in doing something, he will probably create some TikTok showing how "crazy" it is, only because as a foreigner, he's not really going to understand it, and people often try to ridicule and explain things that they don't really understand, thinking they're helping out others who might follow behind them.

Perhaps my story might shed some light on this. In the 1980s, I was in the Army and was sent to South Korea after learning the language in a military language school. 25 years later, I returned to South Korea, doing one of those teacher years, mainly because I wanted to see how much South Korea had changed in 25 years (which it had). The one thing I did notice culturally is that there were a lot of Teacher Luke sorts writing articles and making videos about the "real" Korea, and they were so often more wrong than anywhere near close to correct. What I did notice at the same time is I kept getting a different perspective because I communicated with everyone in actual Korean, and when I did so, I found myself receiving access to a lot more opportunities and explanations of culture than I ever would have had if I'd only just been a young teacher coming over with little to no understanding of the native language. The big difference is that my experience was enriched by the fact that so many more people opened up to me and invited me to outings that were generally kept hands off by most foreigners. However, I also discovered that because I was fluent in their language, I also recognized when I was purposely being shunned from cultural situations, things that were reserved for only people from that country. Other Americans sensed such distance as well, but often attributed it to a hostile mentality towards foreigners, but my understanding of their customs (which I started to learn long after learning the language) helped me realize this behavior was not hostile or negative but something that all cultures participate in as a sort of built-in defense mechanism. The Teacher Lukes would exploit this behavior as funny and worthy of ridicule, never realizing how prevalent such behavior is amongst most cultures.