This study aims to investigate why the Thai EFL learners at Nakhon Si Thammarat Rajabhat University (NSTRU) cannot speak English fluently and examine the internal factors that demotivate them from speaking English either in class or in daily life situations. To achieve these objectives, 316 male and female learners were randomly selected to participate in quantitative data collection, out of whom ten volunteered to be interviewed. The data were analyzed through descriptive statistics and qualitative content analysis. The findings revealed that Thai ELF learners at Nakhon Si Thammarat Rajabhat University cannot speak English because they have difficulties in the four components of speaking skills, i.e., a lack of vocabulary, an inability to pronounce some English sounds correctly due to mother tongue interference, a lack of grammar knowledge, and the perception of being ineloquent in English. They were demotivated to use the language due to four internal factors, including fear, lack of confidence, negative attitudes towards speaking, and the hindrance of unpleasant past experiences.