Evidence of the health system challenges to promoting respectful maternity care (RMC) is limited in Ethiopia and globally. This study investigated the health system constraints to RMC in three Southern Ethiopian hospitals. We conducted a qualitative study (7 focus group discussions (FGDs) with providers of RMC and 12 in-depth interviews with focal persons and managers) before and after the implementation of an RMC intervention. We positioned childbirth services within the health system and applied complex adaptive system theory to analyse the opportunities and constraints to the promotion of RMC. Both system "hardware" and "software" factors influencing the promotion of RMC were identified, and their interaction was complex. The "hardware" factors included bed availability, infrastructure and supplies, financing, and health workforce. "Software" factors encompassed service providers' mindset, staff motivation, and awareness of RMC. Interactions between these factors included privacy breaches for women when birth companions were admitted in labour rooms. Delayed reimbursement following the introduction of fee-exemption for maternity services resulted in depleted revenues, supply shortages, and ultimately disrespectful behaviour among providers. Other financial constraints, including the insufficient and delayed release of funds, also led to complex interactions with the motivation of staff and the availability of workforce and supplies, resulting in poor adherence to RMC guidance. Interventions aimed at improving only behavioural components fall short of mitigating the mistreatment of women. System-wide interventions are required to address the complex interactions that constraint RMC.