It's been a gripe of mine from way back too. Not that there's anything wrong with demoing with a BIT of jazz, but there seems to be a boring sameness in the way reviewers demo the pianos.
Similar to the auto demos in most keyboards actually! (And we know the general public feel this way about those corny inbuilt demos, because when a new keyboard comes out with some less corny demo tunes, they make a noise about it).
I find it's the same deal when demonstrating the sound capabilities. Start with pianos...yes of course, then it's the same old routine of electric piano, organ, bass....when there are often so many other fine patches to choose from. It gives me the impression that the world is mainly into jazz electric piano and organ, and the wider variety of sonic pallet is non existent. I pretty much switch off now, when reviewers go into that same boring routine, including playing just jazz. It also just goes to show how the more that's changed, the more that has stayed the same. New products often boast some great new technology which they go into the same related speel of it being groundbreaking, but in the end, the older tech often sounds better?
There! I said it! As always, just my own view, yes a bit over generalised, but I got it off my chest
Yes the Polish music youtube channel muzykujkropkacom is an exception, I do enjoy their style of demo, musically more interesting than many.