UX design is often treated as the layer that gets applied once the "real" decisions — what the site does, what it says — are already made. In practice, interface decisions are some of the most directly behaviour-changing choices in a website, often more so than the copy sitting inside them.
Where a call-to-action sits on a page, and how visually distinct it is from everything around it, measurably affects how many people click it. This isn't a matter of taste — it's tested, repeatable behaviour. A button that's technically present but visually competing with five other elements for attention will underperform an identical button given clear visual priority.
Every additional field on a form is a small additional reason for someone to abandon it. The instinct to collect more information "while we have them" directly works against the instinct to actually get the form completed. The businesses that ask only for what's essential at each stage consistently see higher completion rates than those that front-load every field they'd eventually like to have.
The reason UX decisions get made through research and testing, rather than internal opinion, is that the people building a website are the worst-positioned people to judge how confusing it is — they already know where everything is. Mapping real user journeys, before design decisions are locked in, is what catches this.
Our UX/UI Design service is grounded in journey mapping and prototyping before full design and development begins, so interface decisions are based on how people actually navigate, not assumptions about what looks clean. See our answer on why UX/UI design is essential for modern websites and apps for more.