Musical tastes are constantly evolving. People enjoy pop music, but it seems like a lot of people are alternatively into the classics. Not just classical like Mozart, but even 40's, 50's, 60's, and 70's music. I was at a friend's house yesterday, and he listened to a wide variety of older music. I think some people just aren't a fan of pop, so they see what else is out there.
As a fan of classical music myself, I do not understand why more people to do realize the genius and brilliance that is classical music. Chopin, Mozart, Bethoven - they have become more popular as they are brought to light. You cannot fail to appreciate the beauty and ground-breaking contributions these artists contributed to the world.
In 2016, a 225 year anniversary edition of Mozart's music topped the sales charts, according to Billboard, by selling 1.25 million CDs. However, the way that happened is worth a second look. The anniversary set contains a 200 CD collection, and each CD in the set counts as an individual sale. Since about 6,000 consumers purchased the anniversary collection, that technically makes it look like Mozart's music beat out all of the popular artists of the year.
The increase in Mozart CD sales doesn't mean musical taste is changing. It just means that there was a trend. Something happened to spark people's interest in Mozart's music. What it was that did this, I don't know, but it is a natural occurrence and I wouldn't read anything into it.