That's not true at all... Look at the infinite number of "Ambient" music streams on YouTube and elsewhere. Just because it's not the music you are familiar with doesn't mean it doesn't exist. This one 4 hour segment has been played 42 million times.
The real issue is that record labels cannot monetize it and therefore there's no cohesive marketing push, which in turn would lead to radio airplay.
That's true. Ambient music is popular on You Tube, although we don't know the age of the people clicking, could be young, could be older.
But instrumental music has been wiped from the radio dial. From the earliest days of FM radio, instrumental stations were popular. Each large market had a commercial classical station and several beautiful stations. Then most markets had Smooth Jazz stations. But now every station on the dial plays only vocals. Classic Hits stations won't play instrumental songs, even those that reached the top ten.
And yes, record labels can't monetize instrumental music. One of the biggest selling jazz albums of all time, triple-platinum Breezin' by George Benson, was all instrumental except for two songs, even though Benson was a good singer. But that was 47 years ago.