Recent years have seen a considerable surge of research on interest-based engagement, examining how and why people are engaged in activities without relying on extrinsic rewards. However, the field of inquiry has been somewhat segregated into three different research traditions which have been developed relatively independently-research on curiosity, interest, and trait curiosity/interest. We identify "long-term development" as a critical factor that links different research traditions, and set out an integrative perspective called the reward-learning framework of knowledge acquisition. This framework takes on the basic premise of existing reward-learning models of information seeking: that knowledge acquisition serves as an inherent reward, which reinforces people's information-seeking behavior through a reward-learning process. Critically, however, the framework reveals how the knowledge-acquisition process is sustained and boosted over a long period of time in real-life settings (i.e., self-boosting effect), allowing us to integrate the different research traditions within reward-learning models. The framework also characterizes the knowledge-acquisition process with three distinct features that are not present in the reward-learning process with extrinsic rewards-(a) selectivity, (b) vulnerability, and (c) under-appreciation. Finally, we discuss implications of the proposed framework regarding the debate over the conceptualization of broad concepts, namely; curiosity, interest, and intrinsic-extrinsic rewards.