It is not a good look that the website does not address the obvious question of "Why should this be trusted to exist in x years".

While that's a fair question.

I'm thinking that you would get same answer if website/company that offered this was Google/Amazon/etc

In fact it might even be worse with those since they keep launching and then few years later "sunsetting" various things.

I believe a Dead Man Switch should be a pattern of “Processes with Information” rather than a service.