Mark Noonan emphasizes the importance of accessibility in front-end application development, particularly in legacy applications, by sharing insights from his role as a product manager at Cypress Accessibility. He notes that accessibility should not be an afterthought and acknowledges the challenges of making older applications accessible, given that many were developed without accessibility considerations. Noonan suggests adopting an incremental approach to improve accessibility, using tools like Cypress Accessibility to automatically detect and address issues gradually. He underscores the significance of understanding the core principles of accessibility, known as POUR—Perceivable, Operable, Understandable, and Robust—and stresses that automated checks, while not comprehensive, are essential in providing fast feedback and preventing regressions. Despite the complexities involved in updating legacy code, he advocates for starting small and building momentum to foster a more inclusive user experience, encouraging organizations to focus on making continuous improvements rather than waiting for a complete overhaul.