Upvote:4
I noticed this too when I was in Thailand. My guess would be that since fast Internet access, the kind that a commercial establishment would need to serve multiple guests, is relatively expensive in South / South-East Asia, they try to regulate access points for maintaining speeds. So for instance in the morning, guests would typically be out, and return in the evening, thus putting greater demand on the network. By limiting the access point to the lobby, it adds extra effort on part of guests to go and use WiFi, rather than everyone joining in from their rooms which could result in a trickle of bandwidth available for everyone.
The other reason could be that bandwidth-limited internet plans are common in South / South-East Asia with limits in 10s of GBs, so it's a way of regulating how many people are using the Internet to ensure they remain below the limit and don't get hit with extra charges.