Why YSK: Because some people may want to use old reddit’s interface and might be used to it’s look. To choose the instance, put a /[instance name] after that url, or use the option given by the site itself
edit: apparently the original site where this came from is https://mlmym.org/ and this is the github repository https://github.com/rystaf/mlmym
Although if that’s a concern, the user scripts could also do that, unless you take the time to go through them completely.