They can be held to account when they fail to deliver what they promise! But what is promised for delivery is what's in the Terms of Service (i.e. the agreement). Nothing more. If it's not in there, you can't hold them to account for it.
> It's too easy for companies to fail to provide their service as long as they never promise to provide their service.
I don't even know what this means. You can't make anyone work for free, nor dictate the terms of what kind of work someone will do without their consent. I assume you are not pro-slavery.
You didn't merely call out their failure. You said it was "too easy," implying something more, like they owe you something. It's a pretty entitled point of view.
"[W]ant[ing] companies to put some effort into avoiding ... failures" is not the same as "hold[ing] them to account". The former is "this sucks and I don't like it." The latter is "punish them or force them to do what I want!"--i.e., some sort of legal remedy.