One way that we've tried to describe it in the past is that Let's Encrypt doesn't actually offer a service which is meant to be used directly by human users, but rather one that is meant to be used by machines and software in order to automate certificate issuance as part of some other function.
Now, "use by humans" and "use by software" are relative, since humans write software and humans use software. But the ideal case for Let's Encrypt is what @_az describes, where it helps service providers (as well as developers of web servers like Caddy) make HTTPs a 100% automatic part of web hosting.
So a lot of replies on this forum have been along the lines of "if you don't like the Let's Encrypt ecosystem's options for your environment, change your environment!".
But there is a community-maintained list which is growing all the time showing hosts with good Let's Encrypt integration.