To the OP. It would seem that you do not have a basic understanding of Thai culture and office 'life'. I have been MD of 4 companies in Thailand since the mid 1990s, although not continuously, as well as working in the offices of many Thai companies.
From my experience it is normal to give donations when asked, buy a small gift for a birthday or share with others, just as it is normal to be invited to or go for lunch with Thai colleagues. This is life in Thailand and if you act like you are you will be alienated, which means that if the staff you refer to are working for you their output may not be what you expect. Have a look at the body language of your colleagues.
It is not much different albeit sometimes in different ways in neighbouring Cambodia and Vietnam.
Open your eyes.