{{Citation needed}}
Amazing how this minhag was forgotten by even the most chassidish Zals and Anash shuls across the globe, where people protest just about every deviation, but never this one.
Please don't take offense to the following, I'm not being judgmental, it's just reality. And I say it with lots of love.
IMHO there are certain things/customs that OOT/BT folk don't pick up in their home, and neither in yeshivos.
I assure you this is not unique to Lubavitch, but to all types of groups in Orthodoxy, each in their own way.
This type of thing is one of them IMHO.
I know this may come as a shock to you, but in general Lubavitcher Chassidim were not very much in to singing during davening.
This mostly began to change in the last decade or two before that fateful day.
I'm referring to all the places in davening your familiar with singing, .לכה דודי, האדרת, קל אדון, ממקומך, ועוד
Even this nuance is likely a gradual change (PCMIIW) that has happened in many other communities as well.
My proof to this is that many contemporary youth don't know the nusach (tune) for the aforementioned תפילות\פיוטים. They are shocked to learn that a nusach even exists (by "nusach", I mean the traditional [maybe even Skarbove] tune used universally by all Ashkenaz), and it wasn't always sung. And this applies to many communities in Orthodoxy in general.
Why you wouldn't have necessarily gleaned this information in Yeshivos, I have a some theories why that may be.
A. Much of the time Davening may be run by the buchrim (i.e. as ש"צ) and they are simply ignorant, and the הנהלות tend not to meddle in, especially since there's no reason to.
B. Yeshiva environment usually is one of guys trying to be (or at least put on a show of being) as frum/chassidish/machmir (pick your choice word) as they can possibly be. So it doesn't exactly create a space that is ripe for the students to be even so much as interested in mellow or lame customs of yore.