In many countries, people don't understand the concept of lifestyle business (even if it brings multiples of salary in revenue, like this case). It is considered "prestigious" and safe to have a job (It doesn't make sense, but it is how it is).
They makes the same amount from AdSense in one month as they do from 15 months of their job. Assuming this has been going on for a few years, I doubt the money from the job is really effecting the size of their financial safety net. If they're spending within their means from the job they have a safety net that will last "forever". If not their real job isn't enough for them anyways.
Non financial reasons for keeping the job could make a lot of sense though.
What happens if he gets banned by Adsense?
In many countries, people don't understand the concept of lifestyle business (even if it brings multiples of salary in revenue, like this case). It is considered "prestigious" and safe to have a job (It doesn't make sense, but it is how it is).