I worked in companies that are committed to Agile and companies that have a completely custom planning and development process. I don't understand your argument. What process in Agile dictates shipping subpar UI?
Build, test, file bugs, resolve bug. You can do this within any framework. Or, better, develop a high quality UI component library instead of asking a junior engineer to write CSS for correct checkbox handling.
Particularly with Scrum, people get hung up on the 'rules' of the 'process'.
For example, following the rules of Scrum, if a developer finds a bug, decides to fix it, and wants to commit the fix such that it can be tested and closed out then that bug needs to first be assigned to the current sprint before the developer can touch it. It's extremely constraining and antagonistic towards shipping good software.
In my experience, unnecessary processes can creep in into any org, regardless of the planning framework used. Agile or no Agile, over-planning cripples teams.
All I can say is if this is the common denominator...