I recall seeing some yes. Yes, it is a thing. A lot of people would be.
There is a problem however which is why this is a much smaller thing than you would expect. The brain when awake interprets sound waves differently than when asleep. The difference is slight, yet profound. Basically it is more important for a sleeping person to be alerted to danger, than it is that the person remember things they hear while in this state. Thus while asleep sound waves that travel on the same wavelengths etc. as when awake simply do not work the same. At best they will wake the subject up, not have a lasting effect.
To have a lasting effect the source audio needs to be modified so that it taps into the dream brain wave patterns. Basically the audio hijacks the dream taking place, inserts the new audio into that dream, and thereby the new audio is "remembered".
The stumbling blocks here is multiple here. First not very many people who release these hypnosis tracks actually understand psychology and brain patterns.
Second, even if you know the correct wave lengths to make tracks so that they hijack or hitchhike onto the dream sequencing it requires special equipment or coding to make the audio adjustments. Equipment and coding training that the recording hypnosis track makers don't have.
Third, is the mindset of "why fix what isn't broken especially if that would cost me money to do?" The popular hypnosis track makers are popular as is without needing to make the financially expensive leap into acquiring the technology to make the new form of media. Therefor they just keep producing the same media and selling it instead.
Fourth, people in general in the community do not even understand that they would need special tracks just for it to work while sleeping. They generally speaking know even less about how the brain works than the previously mentioned ignorance of the track makers. Because they do not know of the required need for specialized production they simply do not ask for it. And if people do not ask for things then they seldom get produced unrequested.