Kenya's 2017 ban on plastic carrier bags, enacted through Gazette Notice No. 2356 under the Environmental Management and Co-ordination Act (EMCA, Cap. 387), is among the most ambitious environmental policy interventions in sub-Saharan Africa. Yet despite penalties of up to four years imprisonment or a fine of KES 4 million, a significant enforcement gap has persisted: illegal plastic bags resurfaced in 14 out of 17 sub-counties in Nairobi by 2023, and over 60 per cent of low-income households in the city continued to use banned bags. This paper investigates the governance dimensions that drive this enforcement gap, examining how weaknesses in Policy Enforcement, Policy Awareness, and Institutional Coordination explain the distance between legislative intent and on-the-ground compliance. The study was anchored on Policy Implementation Theory (Pressman & Wildavsky, 1973), complemented by Institutional Theory, the Theory of Planned Behaviour, and Collaborative Governance Theory. A descriptive research design was adopted, targeting 750 stakeholders from NEMA, Nairobi City County Government, community leaders, market traders, and community-based organisations, from which 261 respondents were selected through stratified random sampling. Data were collected using structured questionnaires and analysed using descriptive statistics, Chi-square tests, and multiple regression analysis. Findings confirmed that all three governance dimensions had statistically significant positive effects on closing the enforcement gap (p < .001). Institutional Coordination (β = 0.40) was the strongest predictor, followed by Policy Enforcement (β = 0.35) and Policy Awareness (β = 0.30), collectively explaining 61.9 per cent of the variation in implementation outcomes. The study concludes that Kenya's enforcement gap is fundamentally a governance gap, and recommends strengthening inter-agency coordination, adequately resourcing enforcement agencies, and institutionalising sustained, participatory awareness programmes.