To understand market equilibria in the platform economy, it is important to consider competition at every level. In the recent literature on platform competition, Karle et al. (2020) proposes a platform competition model accompanied by seller competition in each platform and shows how the platform market structure is driven by the product market competition. In this paper, we extend the model of Karle et al. (2020) and rationalize a process that a platform acquires a dominant position in the market. We specify diverse platform market environments in the model, such as multihoming choices and tastes of consumers, tying, and advertisements on platforms, and analyze how the tipping equilibria and welfare concentration evolve.