By the time a firm has been trading ten or twenty years, the website has a different job than it did at the start. The people looking at it are not strangers picking a name off a list. They are clients comparing your quote against two others, architects checking your finished projects before recommending you, and referrals who were given your name and are quietly verifying it.
Every one of them arrives with your reputation already half formed. The website either confirms it or quietly undermines it. A firm doing serious work behind a dated template site loses nothing loudly: the shortlist just gets made without them.
Builders web design, done for firms at that stage, means building the reputation infrastructure behind your quoting and referrals: the projects, the accreditations, the trading history, all presented at the standard of the work itself. It decides which work you are considered for.