I do not know why Windows version seems to install all those dictionaries either.
Actually I have a list of over 180 dictionaries that can be installed through the Extension Manager. Over 20 of them various localized Spanish versions. They are almost 200 MB in total file size.
Each help pack is nearly 10 MB in size, but do you want to deal with having the download file be 10 MB multiplied by 110+ languages?
I think, since Windows is the most popular version used, the developers may have wanted to have many of the most "popularly needed" languages included in the dictionary list. Why the list is not reflecting the chosen languages, is either a bug or was something that did not happen due to come coding issues.
You never did say what language you use, but I am guessing that it is US English, by your email address.
To be honest, LibreOffice is an "International Version" of a office suite package. It was designed to have one download file for program install, then you install the language and help packs to make it have menus in your needed language[s]. It can be difficult and time consuming for developers to put out a different install version for each language and each OS. It works better if you separate the language in the menus and dialogs out of being "hard wired" to the code and have the languages in a separate section. Then that section is filled with information for the specific language needed. Now, all you need to do to add a new language is to create that separate section and install it. Otherwise, for every language, you need to go into the code and edited all the lines that involve what text is being shown by the menus and dialogs. After that, if you got all the lines correctly edited, you have to do the multi-stepped compilation process for each set of coding for each set of operating system. It is much "smarter" for developers to separate the languages out of the coding so it is faster and easier to add more languages supported.
So why the issue with all those dictionaries showing in the Extension Manager for Windows install? I do not know. At least, for the users that do not use English as their primary language, LibreOffice seems to support more languages than any other office suite I know of. More than MSO and more that OOo [the last time I checked].