Don't try to excuse them.
Poor? They've likely each got a million baht in farmland upcountry and a house, likely have a higher net worth than most farang English teachers here.
Stealing is a vice for some people. Some people like booze, women, drugs, others like to take what isn't theirs.
For others, they get their buzz from playing the wealthy philanthropist when they come to places like Thailand.
The white knight syndrome is strong in you, I see.
Be honest, you are just excusing them because they are Thai. You'd never excuse a cleaner in your home country.
Stealing, scamming, and being dishonest is really ingrained here.