Abstract
This study examines the transformation of global digital advertising markets driven by the emergence of marketplace platforms as dominant advertising channels, comparing EU, USA, Russian, Chinese markets, and utilizing Russia's natural experiment following Google and Meta's 2022 exit to test core assumptions of platform competition theory. Through comparative analysis of market concentration dynamics across major jurisdictions, we demonstrate that the traditional correlation between user attention and advertising revenue has decoupled, challenging established theories of two-sided markets and market definition approaches in competition law. Our empirical findings reveal that marketplace platforms achieve superior monetization efficiency through integrated commerce models rather than traditional attention-selling mechanisms, representing a paradigm shift with significant implications for competition policy and regulatory design. The research contributes by demonstrating that marketplace platforms achieve market dominance through commerce infrastructure control rather than traditional user attention metrics, requiring fundamental revision of market definition approaches in digital platform regulation.