For those outside Indonesia, that figure is indeed hard to believe. Yet, such is the reality. In Indonesia, there are many gambling sites that look unprofessional, unlike Stake, Rainbet, Shuffle & several other big brands. I suspect they compiled the data based on names per domain. Consequently, mirror sites are also included in the records. That explains why the figures are so high.
I understand that that figure is likely true 3.7 million gambling websites is actually achievable if the gambling market in Indonesia 🇮🇩 is unregulated there must be likelihood of several scam casino who just popped up and off just stealing gambler's money in an unethical ways, the Indonesia government have done well; at least this paves the way for people to get access to legit gambling sites around.