Global discussions on the future of high streets, especially today in times of epidemiological, political, and market turmoil, emphasize the importance of high streets as laboratories for urban walkability, resilience, and sustainability. The major condition, however, is a collaborative, cross-sectoral approach towards high street development. Such efforts have been recently undertaken in Warsaw, Poland, to develop a lively but organized shopping street almost from scratch—a few promising joint initiatives with this goal have been undertaken in Warsaw over the last two decades. Building upon a broad document review and in-depth interviews with sixteen pioneers (business consultants, public authority leaders, and planning experts) directly involved in the development of high streets in Warsaw, this study reconstructs and analyzes their efforts in urban collaboration through the lens of Urban Regime Theory. By discussing strengths and weaknesses of the regime structuring process, this paper points at critical difficulties in high street sustainable development (and consequently, also to overall urban walkability, resilience, and sustainability) which are the inertia of mutual perception by stakeholders, dependency on singular leaders and their personal motivation, the necessity to reinvent the very idea of a high street anew, lack of adequate legal tools for cross-sectoral collaboration, and the stiffening effect of previously set guidelines.