This qualitative study explores long-duration energy storage (LDES) technology adoption within the U.S. energy industry. A qualitative approach was selected to uncover subtle dynamics of emerging technology deployment that are difficult to capture using other research methodologies. Recognising the predominant focus in existing literature on technological advancements, policy and market mechanisms, electricity system modelling, and the clarification of the role of LDES, this research addresses a critical gap by emphasising the perspectives of energy project investors and market entities. Through in-depth interviews with industry experts from utilities and independent power producers across the U.S. in both regulated and deregulated electricity markets, the aim is to unravel practical considerations that influence investment decisions in LDES technologies. The principal contribution of this study lies in the synthesis of insights gathered from the interviews and relevant literature, creating a theoretical framework of factors shaping LDES adoption. This framework is organised around six main themes and 20 subthemes, further classified into 102 key categories. The primary conclusion drawn from this structured analysis is the identification of multiple underexplored areas within the realm of LDES. Several of the identified main themes, as well as numerous subthemes and key categories, emerge as subjects necessitating further investigation. This study not only enriches our understanding of LDES adoption but also serves as a catalyst for future research initiatives to delve deeper into these overlooked facets, ultimately contributing to the holistic advancement of LDES technologies within the energy landscape.