Accessibility audits tend to happen at the end — a list of contrast failures and missing labels, handed to whoever has time to fix them before launch. By that point, fixing things properly often means redesigning, so they get patched instead.
It's much easier to choose accent colors that meet contrast requirements from the start than to adjust a palette you've already built a brand around. A quick contrast check during palette exploration — not after the brand deck is approved — avoids the awkward conversation later.
Browser default focus rings get overridden by global CSS resets more often than not, usually without a replacement. Designing an explicit, on-brand focus state for buttons, links, and form fields — and including it in the component spec — means it's far more likely to survive into production.
An icon-only button needs an accessible label. The best time to write that label is while you're designing the button and know exactly what it does — not weeks later, when whoever's filling in alt text has to guess.
None of this takes long when it's part of the first draft. It takes considerably longer when it's a fix list at the end.