Then ExecStop is basically on-cleanup, not to-stop. ExecStart really is to-start, not on-start. In the httpd server case, ExecStart runs the httpd command.
I think part of the problem is with how one "naturally" or "habitually" thinks of a Service. From systemd's perspective/terminology, the Service is the thing that starts and stops. But whether because it is inherently more intuitive, or because of how daemons traditionally worked on *nix, the mind tends to think of the process which the Service starts as the thing which starts and stops. I'm not able to double check currently, but I also think that systemd isn't totally consistent with the mental model it bases the choice of keywords on when it comes to ExecStop, because with that mental model one would expect ExecStop to only run when the Service is stopped from systemd, but I'm fairly sure it runs in other cases when the process started with ExecStart exits, but the service isn't necessarily stopped. I could be wrong about that though.
If that helps you understand it better, then sure.
All I am trying to say is that the name of the option makes sense as-is: it literally runs the provided command(s) on service stop (“execute on stop”).
Similarly, ExecStart literally means command(s) to execute on start.
If the command runs a blocking daemon/server (usually the case), then the server will be implicitly stopped by definition - because if you’re stopping the systemd service, you’re interrupting any commands that are still running/blocking.
