Don't underestimate the number of digital pianos that are being sold, they don't have to be tuned regularly which substantially reduces the cost of ownership and they tend to be a lot smaller and easier to move around. The quality of the latest batch is excellent. I have both an acoustic and a digital one and to be fair the acoustic is half a century old and sounds better up close but for practical reasons I find myself playing the digital one much more often using headphones so I don't disturb others.

Even so, you are right, it is definitely not a growth market by any stretch of the imagination, it takes a ton of effort to learn how to play and in a world full of distractions and ready made music more than you could ever listen to in a lifetime the enthusiasm for doing this is waning. There are exceptions to this though, for instance, in Asia where playing the piano is a status thing and still in its ascendancy phase.