That said, Tailscale is one of the products that just works.
Maybe a slight bias on my part as I'm a developer and not an investor.
And not that funding or advising is less important, but it's a nice feeling connecting a product I like to faces who make it happen.
1. Potential customers
2. Potential investors
Both groups are a lot more swayable by social proof from seeing the "investors" than the devs as they infer a lot of credibility based on who has funded you. Similarly that's why you often see big company logos on marketing pages because it makes other customers more likely to buy. "<xyz> is too big to be wrong about this product"
Putting people on the website is, very variable. Do you update the website every week or two when someone comes or leaves? Well that's awkward if someone is fired.
You get to 100 people, then 200 people. Now what do you do? Remove everyone? Only put people on above a certain level? What do you do when someone asks you not to be listed. Or when John becomes Jane, but doesn't want to be super duper public about it?
Or, when your company gets media attention and now the moment you add/remove someone from the website you get news or social media posts about it?
They're not exactly secretive, there's just little value to have it on the main company page. (And if you just want pictures, https://tailscale.com/careers has that too.)