The main factor was the extremely low pay. Weird schedule too. (I worked in a conversational school, so not really even a teacher). Unless you work in international schools, you won't be making much more than minimum wage. It's a lot of fun though. I'd happily do it for possibly my whole life if the pay was better or I had another source of passive income.
You can also teach your skill. I do that, although not full time, but there is money to be made. If you are reasonably good at your craft you can teach novices and you can make sure they get their money's worth. Or give training at a company. I teach creative coding for lighting designers and vj's and if I could do it every day of the year it would net me a good income. However, the market is too small to live off.