I think it is also a huge issue that there is no methodology or virtuoso pieces to aim at in order to spend hours a day practicing on the Push.
I grew up playing classical guitar and use to own a Ztar and this was the issue I had with it. My guitar chops transferred to it pretty nicely but it is still its own instrument. Own instrument with no music or practice material, no transcriptions of anything other than what you come up with yourself.
How far would anyone get learning piano if they had to also come up with the music and practice material outside of drilling scales concurrently with learning the instrument itself? It would just be a nearly useless gimmicky instrument.
It's a fair point, but it's not a completely barren landscape. Melodics (https://melodics.com/) is one platform aimed at developing pad controller skills. For a much more rigorous and far less marketing-driven approach, I really recommend Quest for Groove (https://questforgroove.com/) which develops a lot more than just the physical dexterity required to drum on one of these things.
As with anything, it does just take practice, and these instruments are so much easier to play than something like a guitar that just noodling around will also get you places.
But that initial barrier is such that a beginner will be able to get much more mileage out of such a device. They might never even run into the limitations though it may limit the musical space that they can work in on some dimensions.
In the end what matters is the result, not so much how it was reached.