Because the editor constantly breaks HTML by forcing its own formatting rules on it which breaks substitutions so we never made it an editor. It won't do that unless it's specifically configured not to do that, but that's not the case for default installs so users would add complex substitutions to it which wouldn't work. It supports HTML though as noted in the parameters description. We may change it to an editor in the future as this likely isn't a problem now since we've made improvements to our substitution code.
is it possible to use default custom module joomla and use subsition in that?
Use substitutions in a Joomla HTML module? Yes if you've CB Content Bot installed and you've enabled content plugins for the module.
is it good to use cb replacer bot ?
Don't understand what you're asking. It's just a tool for replacing X with Y.