As advancements in artificial intelligence (AI) technology have opened new avenues for artistic expression and creation, human-AI collaboration in creative activities has garnered increasing attention. Through semi-structured interviews with 15 participants, we investigate the intrinsic and extrinsic factors that motivate laypeople's engagement with AI painting, as well as challenges and concerns faced by users. Our findings reveal that laypeople engage with AI painting for emotional needs like entertainment, aesthetics, surprise, and curiosity, personal utilitarian needs such as self-expression and customization, and social interaction through sharing and communication. Despite the appeal of novelty and unpredictability they also encountered challenges related to technical and system functionality, personal and environmental factors, as well as concerns about algorithm bias, pornography misuse, employment risks, copyright disputes and ethical implications. Findings provide preliminary evidence of the potential and limitations of AI in democratizing creative activities, and offer implications for designing and developing of AI assistance tools.