Note the aveilus observed during the Three Weeks (Bein Hameitzarim). At the end of Masechta Ta’anis, there is about one blat relating the halachos pertaining to Tisha B’av and the “shavua she’chal bo.” Yet in Tur and the Shulchan Aruch, we find many simanim on this topic, extending the availus back to 17th of Tammuz. The GRA writes that the Gedolei u’manhigei Hador at certain times, saw fit to add some chumros. This is due to the influence of the “airev rav,” who have always been present, and exist even today among us although their exact identity is unknown.
Even the chumros in tahara that “women accepted upon themselves,” with all due respect, became halacha pesuka only when the chachmei hador make it a takana. Which is what it is nowadays.
Only on certain matters of minhag, did the chachmei hador say “puk chazi mai dovar (or avid) alma” — “go out and determine what is the prevailing custom.” But, not when it comes to halachos, de’oraisa or even de’rabbonon.
So, Chumros decided upon by the Gedolei Hador are part of halachah today. Whereas chumros dreamed up by (often) bored folks, many of which have various social agendas besides enhancing Torah observance, are not and cannot be included in today’s body of halacha. No one has the authority to make takanos today. On occasion and as needed, the gedolei haposkim of our times have ruled le’hachmir on many matters. It is not our place to try to get into their holy minds and second guess their intentions why they paskened the way they did. If a certain group or community wishes to follow a particular stringency, and their rav/rebbe/poek concurs, so of course, there’s nothing wrong and everything right about it. But beyond that, we need to consult the gedolei poskei halacha how to conduct ourselves.