Most nonprofit sites were built once, by a volunteer or a board member's nephew who wanted to help. Then nobody touched them again. The mission gets buried under a slideshow of stock photos. The donate button hands the visitor off to a third-party page that tracks nothing about who gave, or why.
Meanwhile, the people deciding whether to trust you are doing their homework quietly, without ever calling. A donor sizing up whether you're real. A volunteer trying to picture themselves showing up. A grant reviewer or program officer checking you out before the first conversation.
SO. The website has to do a job nobody assigned it: prove you're legitimate, explain the mission fast, and make giving, volunteering, and following up easy to measure. That's a different job than "get us online." It's the job a custom nonprofit website is actually built for.