Mta88 I would assume they are perfect for high humidity climates like the tropics etc?
Not at all. Acrylic pianos are plastic only in the case. The soundboard and the action are traditional wooden ones, susceptible like all the others to humidity issues (and arguably even more, since the acrylic case may facilitate condensation and/or desiccation with temperature swings not associated with humidity problems)
If you care about that issue, the perfect solution is a Phoenix piano, which has a carbon fiber soundboard and (WNG) action. The case remains normal wood, and that's irrelevant. I never had the pleasure to try one or listening to one live, but I know that reactions range from "fantastic", to "meh", to "horrible", with the latter usually blaming the agraffe, rather than pins, on the highest octaves of the bridge (in fact to address this issue the company now offers a version with regular pins on those octaves -- they cannot offer pins everywhere because of the mechanical characteristics of carbon fiber compared to wood).
Back to the acrylic piano, it's a style and look which may or may not be liked. The prices are higher and the resale value is lower (since less people like it), so there is little incentive to purchase that version in the first place unless you really like it. Probably they could make a polyethylene version in black which would match the look of traditional "polished ebony" look (which is neither polished nor ebony, but that's the name the industry has agreed upon). I am not aware of any such instrument, even in short run by experimental builders of which there is no shortage, such as the "flying piano" and many others.
I think part of the reason, for both the acrylic and other polymers is that plastic is seen as a "cheap" material and wood as a "premium" one. This is reinforced everywhere, not necessarily true for most modern plastics and I really hate it (for example I did not want a car with "wooden decorations" and it was really hard to find one, because most models have such "premium" features -- until they fade, warp or worse in the harsh weather/temperature conditions a car is often left in - which made the problem really serious for me, since I buy cars of 5-10 year of age and I keep them until they are 20-25)