The bank is not buying the house.
I'd imagine the bank has an outstanding debt to collect, ie if they leant 3M baht to the people buying the house and they've only paid back 2M and stopped paying then the bank is out 1M ( plus any interest ).
Normally bank sell the house just to cover outstanding debt and any costs involved.
It's a nice little earner for the bank managers and they're cronies, as they'll get inside info when the repossessions are happening, get a cracking price and then re-sell on the open market.