I think that one of the important reasons that many Thais do not speak English fluently is the fact that they do not have much possibilities to practice speaking and listening in daily life.
In many mixed domestic environments, the Thai spouse is often able to speak English at an acceptable level within a relatively short time, which proves the importance of “sparring”. The latter goes for speaking and listening, because writing and reading need an extra investment. Sad enough, many spouses see that as a waste of time.
Things in Thai “retail land” nowadays are much better than 7 years ago, when I visited Thailand for the first time.
Nowadays many of the large stores and even smaller ones often have at least one staff member, whom can speak English.