Because everybody and their uncle buys computers, and next to no-one buys high end arrangers.... Economy of scale, pure and simple. Arranger players, in the US at least, are a diminishing market, as manufacturers refuse to add features and sounds and styles usable by younger players, and us older users keep dying off

Computer users are a growing market, with no end in sight.

You might remember, this is what happened to the organ market, which gradually went upscale as it's main users got older and fewer, until it, for all practical purposes, completely disappeared when it got to the point that no-one but the wealthy dilettantes could actually afford one.

The lesson here is, the arranger HAS to evolve, and involve younger players, or it will go the way of the Elka and the Lowery, IMO...