There are reasons they don’t want you speaking Thai. They don’t want you understanding what they are saying about you and they don’t want you understanding what they are planning for you, evenings out etc. Especially if it’s about money. They don’t want to be caught out by a secret Thai speaking falang. As far as they are concerned the less Thai you speak, the better.
The other problem, as pointed out, is the number of regional dialects, particularly in places like Pattaya. Can you imagine a Thai in London, who is able to speak and understand basic English, being confronted by someone with a broad Irish or worse an acute Scottish accent? No chance!
Same applies to us in Pattaya.