Accessibility gets treated as a compliance task near launch, which is the most expensive moment to discover that your component library cannot be operated by keyboard.
Most of it is decisions, not work
- Choosing text colours that meet contrast — free at design time
- Using a button element instead of a styled div — free
- Deciding focus order alongside layout — free
- Target sizes of at least 24 by 24 pixels — free
None of those cost anything if decided up front. All of them are expensive once a hundred screens depend on the wrong choice.
Automated checks catch a minority
Automated tooling finds perhaps a third of real issues. It cannot tell you whether focus order makes sense, whether an error message is understandable, or whether a control is reachable at all. That needs a keyboard and a few minutes.
It is also just better engineering
Semantic markup, sensible focus management and honest contrast produce interfaces that are more robust for everyone — on a bright screen outdoors, on a trackpad, in a hurry.