"But seems it became that younger people just seemed no longer able to get into instrumentals."
Young people are still into instrumentals, however its in the form of EDM, techno and trance.
As a side note, according to Wikipedia:
Trance music - Wikipedia
Trance music is typically characterized by a
tempo between 120 and 150 beats per minute (BPM),
[7] repeating
melodic phrases[7] and a
musical form that distinctly builds tension and elements throughout a track often culminating in 1 to 2 "peaks" or "drops".
[7]
This reads like a modern derivative of Muzak's Stimulus Progression formula.
What's changed is the overall construction of music.
Barry Manilow talks about the challenges he faces with writing music for the current time in this recent interview (around the 5 min mark):
This spoof here also makes an interesting point: (Gimme Some of That) Ol' Atonal Music - Merle Hazard feat. Alison Brown
It's poking fun at the avant-garde classical compositions in a world where "Bach and Chopin" are "melodic and passe."
We can make the same criticism of today's pop lacking in melody...
What made the BM format work was the melody in the pop hits which gave material for the arrangers to weave their magic. Without new melodies, there is nothing for the arrangers to work with. Manilow talks about this.
"Modern" is always relative to the past. There's nothing new. The classical composers from the romantic period would feel the same way about the dearth of melody. Musical styles however comes and goes.