Maybe it's just that I can buy a top-of-the line yamaha motif that plays really well, can be carried to gigs, has dozens of other functions, and (most importantly) never needs tuning, all for fraction of the cost has something to do with that number?

I've owned several pianos... I won't again, if I can avoid it. Just keeping an instrument in tune is enough of a problem: there is one tuner in my area who can get the thing in tune, and I don't like how he does his intonation.

I understand that piano production is way down from the early 20th century, but it's not like there aren't other instruments which have replaced it.

And, further, unlike instruments like the Fender Rhodes piano or the Hammond tone-wheel organs, these things are both still being produced and will in demand for the foreseeable future.

I also play pedal steel, and it is a similar situation: they make a lot fewer instruments these days because there are a lot of alternatives, but there is still more demand than output.